Abstract: The large-scale integration of renewable energy significantly reduces the inertia of the AC system, and the participation of grid-connected converters in the frequency control has become an important means to improve frequency stability. Based on the transfer function model, the dynamic inertia of grid-connected converter with additional frequency control is derived. It is observed that the dynamic inertia exhibits time-varying characteristics due to the combined influence of inertia design parameters and other control elements. However, simplifying it to a constant similar to the rotational inertia of synchronous generators will lead to analysis errors. Therefore, for the two mainstream grid-connected converter control methods of constant DC voltage control and constant power control, the quantitative evaluation method of dynamic inertia for grid-connected converter with additional frequency control is proposed. The influence mechanisms of different factors such as control parameters, operation conditions, and system characteristics on inertia are analyzed. It is concluded that the outer loop of active power control will significantly change the original design inertia, and it is necessary to focus on the inertia deviation caused by its control parameters. Finally, based on the time-domain simulation model built in Simulink, the correctness and effectiveness of the transfer function model and quantitative evaluation method of inertia are verified.