Abstract: In order conveniently calculate the average power of the pendant float of a pendant wave energy generator conveniently, the existing design calculation methods are investigated. Based on the wave theory and the Froude-Krylov assumption method to solve the wave force, the forced vibration theory of single-degree-of-freedom damped system is applied, the wave excitation force is taken as the input power to the pendant float, and the electromagnetic resistance of the generator is taken as the main damping force, so that a mass-spring-damped vibration mechanics model is established, and the computation method of the response of pendant float is determined, and a computational example is given for the pendant float Power Take Off (PTO) system of the actual wave energy generating device. A calculation example of the Power Take Off (PTO) system of a real wave energy generator is presented. Based on the example, the assumptions are expanded, the frequency response curve is applied, and the MATLAB tool is used to make a three-dimensional curve of the average power and a table of the output average power values under different parameter conditions, which clearly show the system response condition. The study shows that under the condition of certain wave height and frequency ratio, the average mechanical power of the PTO system has a peak value with the change of the floating body mass and damping moment, and the design of the parameters of the device around the peak region can achieve more satisfactory results. The modelling and calculation method can provide a reference for the optimal design of practical engineering.