As one of the renewable energy, the absorption and utilization of wave energy is always an important research field home and abroad, and energy absorption efficiency is the key. A wave energy absorption system based on inertial pendulum is presented, and dynamics equations are established. Artificial Neural network with learning rate adaptation is adopted to model in time domain. The results obtained by simulation software and by BP neural network are compared, which validate the method used to be correct and make basis on future research.