Abstract: In this paper, the hydraulic drive system is replaced by the direct drive of the permanent magnet synchronous motor with the screw which connected to the rotor, because of the low transmission efficiency, oil spills and most likely a fire when working in high temperature environment.The parameters of an excavator boom cylinder are converted to the parameters as P_N = 22kW、n_N = 750r/min of the permanent magnet synchronous motor. The 6-pole 36-slot and 8-pole 48-slot motor are designed respectively, the no-load simulations is done in Maxwell at the same time. Air gap magnetic flux and cogging torque are optimized by the way of the use of the uneven air gap, the load simulations is achieved, and a permanent magnet synchronous motor that can be used to replace a hydraulic cylinder is also achieved.