Abstract: At present, there are no unified design standards and criteria for the plugs, so the design length of the most of plugs is too safe. In this paper, relying on Jinjiaba hydropower diversion tunnel plug project, a 3D finite element model for the plug and surrounding rock is established by use of ANSYS software, and the mechanical effects of the plug are analyzed comprehensively. Analysis results indicate that the plug is under pressure, and that the tension and compression stresses are smaller and no more than strength of the plug concrete itself. Cohesion and friction on the contact surface of the plug and the surrounding rock have shared the water pressure. On this basis, an additional resistance of the surrounding rock is taken into account, and design influences of the plug, such as a grade of the surrounding rock and the plug concrete, and a wedge angle of the plug are analyzed. The analysis results show that the proper wedge angle is the necessary condition to take advantage of the additional resistance of the surrounding rock; and the improvement of the grade of the surrounding rock is beneficial to the stability of the plug, but the improvement of concrete strength grade does not improve the anti-sliding stability of the plugs.