Abstract: According to the structure and working principle of the move-in-soil manipulator of the underwater robot, the finite element model has been set up. The straight working behavior of the manipulator in soil is analyzed by means of elastoplastic finite element method. The effect of the degradation area disturbed by the manipulator’s arms in soil on the working behavior is studied. Combining analysis and test results, the conditions under which the manipulator can go forward constantly in soil are proposed.