With the further development of the research on the underwater robot,its motion ability has been gradually strengthened from the simple translation in the early stage to the space motion with multiple degrees of freedom,and the study of dynamics is the basis of the study of other abilities. In order to study the motion of a multi degrees of freedom underwater robot,the dynamic equation of a certain type of eight-thruster underwater robot is modeled,and its motion equation on 6 degrees of freedom is obtained. On this basis,the motion simulation and performance analysis are carried out,and the motion performance of the underwater robot in 6 degrees of freedom is obtained. Through the result of simulation,its movement ability is understood intuitively.