The invention provides a control method and system of an inertia generator, and the method comprises the steps: switching on a start control switch, measuring the voltage information and current information of a power grid, and calculating the actual active power; calculating the frequency of the power grid according to the measured voltage information; determining reference active power accordingto whether the frequency of the power grid exceeds a threshold value or not; and based on the reference active power and the actual active power, realizing active control of the current source type inverter circuit. According to the technical scheme provided by the invention, the rapid control capability of power electronics is exerted; when the power grid frequency is reduced, the rapid active support of different degrees can be generated according to the power grid frequency deviation condition, the response speed of primary frequency modulation is improved, the power grid frequency can bestabilized in an allowable range as soon as possible, the system stability is improved, and the electric energy quality is improved.