Productized bearings can be applied to servomechanisms in space with different loads by adjusting the bearing preload, and this can helps reduce cost and improve succession. Firstly, in accordance with the relationship between preload and friction torque, the factors influencing preload in the bearing assembling process were identified and an equation was developed. Subsequently, the bearing′s interference fit was simplified to a thick-walled-cylinder model and the relevant equations were deduced. Further, based on Hooke′s Law and the definition of Young′s Modulus, the mathematical relationship between the bearing preload and force loaded on the shaft end was deduced. Based on the above steps, a method to control the bearing preload during assembly was proposed. Finally, experiments were conducted to evaluate the control method, with support from a satellite project fund. The results of the experiments indicate that the proposed method can control the bearing preload well. Errors corresponding to the clearance-fit and interference-fit conditions are 2.6% and 20.3%, respectively. Furthermore, towards the end of their lives, the angular-error motion and friction torque of the bearings assembled using the proposed method are 3.04″ and 25.8 mN·m, respectively, and these values satisfy the usage conditions of space servomechanisms installed in satellites.