Abstract: Aero-engine main shaft bearings are subjected to extreme working conditions such as high temperature, high speed, heavy load, lean oil, and oil cut-off. The failure problems such as fatigue and wear seriously affect the reliability of the engine. Therefore, it is extremely important to effectively and accurately monitor the use status of the main shaft bearing of aero-engine. The working conditions, main failure modes and failure mechanisms of the main shaft bearing of aero-engine are sorted out; according to the condition monitoring methods and technologies of the main shaft bearing, the existing main shaft bearing vibration, oil state, sound, acoustic emission, temperature, etc. are summarized and comparatively analyzed. The advantages and disadvantages of other monitoring methods are discussed; the monitoring method and technical characteristics of spindle bearing condition based on multi-sensor information fusion are discussed. The results show that the influence of the material and structural characteristics of the spindle bearing on the output signal of the sensor, the miniaturization and wirelessization of the sensor structure, the efficient multi-sensor information fusion and decision-making method, and the data interaction between the physical model and the digital model will become the main shaft bearings. The main research direction of condition monitoring in the future. The Dn value (the product of the inner diameter D and the rotational speed n) of the main shaft bearing of aero-engine (hereinafter referred to as the main shaft bearing) can reach more than 3×106mm•r/min, the contact stress can reach more than 2 GPa, and the temperature can reach more than 220 ℃. Compared with ordinary bearings, the spindle bearing has higher rotational speed, larger load, severe cage impact, more frictional heat generation, higher working environment temperature, difficulty in ensuring good lubrication, a wide range of working conditions changes in a short period of time, some Severe slippage, etc. The service process of the spindle bearing is actually the friction behavior of two rough surfaces. Vakis et al. [1] discussed the friction behavior of the two rough surfaces under the complex influence of physical, chemical, and mechanical loads, and considered that in the tribological model, it is necessary to consider Complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication, and surface chemistry still require continued efforts. Friction between rough surfaces can cause bearing failures such as fatigue and wear. The bearing structure of each fulcrum of aero-engine is obviously different, and the failure performance is different. The service state of the bearing is the result of the combined action of many factors. Internal factors include materials, surface properties, etc., and external factors include lubrication state, load, and rotational speed effects. Fatigue limits the ultimate life of spindle bearings, but early abnormal failures still account for the majority [2]. Bearing materials are continuously improved to meet the requirements of advanced aero-engine main shaft bearings. For bearing materials and combinations containing different elements and different ratios, their wear resistance and failure mechanisms will change [3-4]; Wakiru et al. 5] It is believed that the lubrication state monitoring can be used as a fault early warning for mechanical equipment, and the lubrication state monitoring of the main shaft bearing is of great significance for fault prevention; the rotational speed and load of the main shaft bearing are the main factors affecting the failure, and the number of bearing rolling elements, the relative relationship between the inner and outer rings. Location, contact stress, slip rate, temperature of the contact zone, etc. all have an effect [6]. The main parameters detected for judging the service state of the spindle bearings include vibration [7-9], sound [8], acoustic emission [10], lubricating oil [11-12], temperature [13-14], etc. High-end equipment is usually installed with multiple sensors, and a more comprehensive and complete description of its status can be obtained through multi-sensor information and information fusion algorithms. 1 Main failure modes of main shaft bearings Main shaft bearings operate under extremely harsh working conditions and complex environmental conditions, and the failure forms are very complex and multiple failures may coexist. The main failure modes of spindle bearings include fatigue, wear, thermal damage, slipping damage, cage failure, etc. [15], as shown in Figure 1. Fig. 1 Main failure modes of aeroengine mainshaft bearings[16⁃18] 1.1 Fatigue fatigue is divided into surface origin fatigue and subsurface origin fatigue. Surface-originated fatigue refers to the fatigue of the surface under the action of cyclic pressure exceeding the fatigue strength or due to the attack of hydrogen ions; the fatigue of subsurface origin, which is related to the maximum orthogonal shear stress. The L-P (Lundberg-Palmgren) theory [19] can estimate the bearing fatigue life. On this basis, the basic formula of the I-H (Ioannides-Harris) life theory applicable to the spindle bearing is shown in Eq. (1) [20] ] where △Sk represents the survival probability of the unit volume, N represents the number of stress cycles per revolution, τ represents the shear stress under the contact of the raceway, τu represents the fatigue limit shear stress of the material, △Vk represents the unit volume where the stress acts, zk represents the depth of stress action, and e, c, and h represent the Weibull parameters determined by experiments.