A 3-DOF mechanical leg with compact structure, strong carrying capacity and the rotational motion in decoupled was proposed. To analyze the drive parameters of the 3-DOF parallel mechanical leg, a dynamic model was established and the peak of a servo motor was predicted based on the dynamic model. Firstly, by analyzing the motion parameters of the leg mechanism, the dynamic model was established based on the Lagrange equation, and the drive force acted on the mechanism was given. Then, based on the dynamic model, a peak prediction model of the servo motor for the drive speed and torque was defined. Finally, for a given motion equation and a set of structural parameters, the time curves of drive speed and torque were obtained, the dynamics of the mechanism was given and the peak prediction model was proved to be correct. Calculations show that the peaks of the drive speeds from three driving motors are 19, 17, 27 r/s for Nx , Ny and Nw , and the peaks of the drive torque are 5.8, 3.1, 4.4 N·m for εx, εy and εw respectively.