A 1:1 scale test platform was constructed to accurately simulate the working conditions and flexible constraints of wind turbine bearings. The research focuses on the main bearing of a 4.5MW wind turbine, where a finite element model of the main shaft system is established. The impact of ring deformation, load conditions, and bearing geometric parameters on the contact characteristics and fatigue life of the main bearing were investigated under the flexible constraints imposed by a hollow main shaft and thin-walled bearing housing. The results indicate that in comparison to the rigid ring model, the fatigue life of the main bearing is reduced in the case of the flexible ring model. Additionally, the location of maximum stress occurrence has shifted towards the larger end of the roller when compared to the rigid ring model. The contact load in the primary load-carrying region of the main bearing increases with radial load and tilting moment, while the contact load in the non-load-carrying region exhibits an inverse relationship. The number of carrying rollers increases with the increase of axial load, leading to a decrease in the contact force of the bearing. However, once all the rollers are loaded, the contact force increases proportionally with the axial load. As the contact angle increases, the contact load of the tapered roller bearing (TRB) decreases. As the radial clearance increases in the positive direction, the contact stress of the bearing increases and consequently leads to a decrease in fatigue life. The fatigue life of the bearing can be increased by applying a negative clearance or axial preload of approximately -0.5mm. The increase in interference between the inner ring and the spindle leads to a reduction in bearing contact stress, thereby enhancing its fatigue life.