Abstract: Traditional motion controller for AUV targets at single degree of freedom (DOF) to decouple in decoupling control, so it ignores the coupling effects of each DOF and makes the control effect not satisfactory in the complex navigation state.In order to improve the coupling effects, a novel motion PD controller is designed.This controller is constructed on the hydrodynamic model of AUV's six-DOFs and simplified according to the practical needs.It uses one motion control equation to realize the control in four-DOFs.Because of the number of the control parameters is so large, it is hard to adjust them by manual.So modified Particle Swarm Optimization (MPSO) is used to determine the parameters of control equation to improve efficiency and reduce the bad effect caused by subjective factors.The last based on the simulation platform of a certain plant-AUV, simulation experiments are conducted for the proposed controller and the results show that the presented controller is feasible in application to AUV.