The invention relates to a preload applying structure and applying method for an integral limited angle torque motor bearing. The method comprises the following steps: S1, assembling a central shaft,a first bearing, a second bearing and a rotor assembly; S2, screwing an inner locking nut and an outer locking nut onto the shaft-end external thread section of a center shaft, adjusting the nuts to the optimal positions and marking the positions; S3, disassembling the inner locking nut and the outer locking nut; S4, installing the inner locking nut in a rotor assembly and screwing the inner locking nut to the bottommost position of shaft-end threads, uniformly smearing thread paint onto the shaft-end threads, slowly and anticlockwise rotating the inner locking nut outwards, allowing space between the threads of the inner locking nut and the shaft-end threads to be fully filled with the thread paint, and then slowly screwing the inner locking nut to the bottom of the threads; S5, uniformlycoating the threads of the outer locking nut with the thread paint and assembling the outer locking nut to the shaft-end threads; and S6, anticlockwise screwing the inner locking nut outwards, clockwise screwing the outer locking nut inwards, locking the inner locking nut and the outer locking nut oppositely and adjusting the inner locking nut and the outer locking nut to the initial marked positions respectively. The preload applying structure and applying method of the invention achieve good anti-loosening effect on the bearing.