In order to reduce the disturbance torque during the assembly of the seeker’s servomechanism, a drive torque measurement system of servo-mechanism was built on the basis of electrical measurement. In the process of precise assembly and adjustment, the drive torque was measured in real time and the assembly parameters were adjusted to reduce the disturbance torque. The characteristics of the mass unbalance torque and the moving cable torque in the driving torque were experimentally verified, and the balancing and routing methods were determined. The relationship between the preload of the bearing and the friction torque of the servo mechanism was also experimentally verified. It is of great significance to solve the problem of automatic running process to reduce the fluctuation amplitude of the friction torque. The method of measuring the rotation error of the rotating shaft is determined, which can be used for determining optimum preload of bearing. Results show that the traditional assembly process of servo mechanism is optimized, and the qualitative method based on the experience of technician′s experience is optimized as a quantitative method.