The present invention relates to energy source absorption and conversion technology, and is especially wave energy absorbing and converting method and system by means of inertial pendulum mechanism. Based on the inertial pendulum energy absorbing mechanism, the inertial pendulum mechanism is driven by waves to move to absorb wave energy and drive a transmission mechanism to convert and store mechanical energy, and the mechanical energy is then released in an energy releasing device. The wave energy is obtained and utilized autonomously, and the amount of the absorbed energy may be estimated based on a wave energy converting and calculating mold. The present invention provides one completely new technological route for obtaining wave energy from sea.