Abstract: With the development of economy, hydraulic transmission is an indispensable part of national economy. Hydraulic actuator is the core part of hydraulic transmission, and the gear motor has the advantages of small size, light weight, and strong adaptability to the harsh working conditions, and has a very important role in hydraulic actuator. But gear motor's torque fluctuation is larger, and there are unbalanced radial force, trapped oil phenomenon and big noise, so it is difficult to develop. Based on these reasons, in this paper, a force balance type multi input gear motor is proposed, which has 3 internal motors and 3 outer motors in one case, the inner and outer motors are evenly distributed on the output shaft, and the radial force of the output shaft is balanced by the output shaft, which can significantly reduce the total force on the gear shaft and the bearing, and help to improve the service life and the mechanical efficiency of the bearing. Each motor has an independent oil distribution device, their work does not affect each other, and a motor can output 4 kinds of torques and rotational speeds through different connection modes as follows: The internal motor works independently, the outer motor works separately, the internal and external motors work together, and differential connection of internal and external motors. As an actuator, hydraulic motor's torque and rotational speed can be achieved with the function of the liquid pressure which the hydraulic pump provide, and the hydraulic motor output torque ripple is an important indicator to measure the performance of hydraulic motors. And it is an important index to measure the stability of hydraulic system. The torque ripple of a single gear motor is related to the number of teeth of the meshing gear, and when the motor rotates one tooth, the torque has a pulse. The force balance type multi input gear motor has a plurality of motors at work at the same time, which is different from the torque ripple produced by a single motor working. When the internal motor is working independently, the difference of the position of the initial meshing point for the 3 internal motors is successively one third of tooth. By the superposition of the torque, the torque ripple of the 3 internal motors can be reduced, but the torque pulsation cycle is changed to 1/3. When internal motor and outer motor work together, on the basis of the same pulse period of the internal and external motors, the position of the initial meshing point of the inner and outer motor gear teeth is different from that of the gear teeth, the maximum value and the minimum value are added, and the torque ripple is minimized. For differential connection of internal and external motors, the motor is equivalent to the pump; under the same pulse period, the position of the initial meshing point of the internal and external motor is the same, and the input flow of the internal and outer motor is offset by each other, so as to minimize the torque ripple. Therefore, when working with a single motor, the torque ripple is related to the number of teeth in the meshing gear, and when a plurality of motors work together, the torque ripple is mainly related to the torque pulsation period of the motor and the position of the initial meshing point of the motor.