The inner curve water hydraulic motor uses high pressure water to push the piston. The roller on the upper part of the piston acts on the inner surface of the stator rail, and drives the rotor to rotate through interaction, thus making the motor run. However, when the roller contacts with the stator rail, self-locking often occurs, resulting in the motor can not work properly. In order to solve the self-locking problem, the pressure angle of the roller in contact with the stator was analyzed, and the contours of the stator curve before and after improvement were compared. The amplitude and angle of the stator were set again to obtain the new curve equation. The stator curve was generated by programming with MATLAB, and the three-dimensional software was used to establish the stator guide rail model. The new stator curve effectively avoids the self-locking phenomenon.