For the complex characteristics of wave and the fully-enclosed wave power generation system，a control algorithm which is robust to wave changes was proposed based on interconnection and damping assignment passivity based control (IDA-PBC)． Firstly，a Euler-Lagrange (EL) model was established for fully-enclosed wave power generation system，and the model was decomposed based on the structure and dynamic characteristics of the sys- tem． Then，according to the Lyapunov stability and damping injection，a passivity-based control law was acquired． In addition，in order to maximize power generation，the desired control objectives were deduced． Lastly，a fully-en- closed wave power generation model in Matlab/Simulink simulation environment was built，and simulation analysis of passivity based control was carried out． The result shows that asymptotically tracking control objectives can be a- chieved，and the control law is also effective in case of wave changes．