Abstract: The extensive access of power electronic interfaced loads(E-load) has an important impact on the characteristics of the composite load and the safe and stable operation of the power system. An equivalent inertia for E-loads and its identification method are proposed to quantify the duration of the transient process under external voltage disturbances. Firstly, a simplified model of E-load is proposed. Then, the definition of the equivalent inertia of E-load and the measurement-based identification method are proposed. Based on the measured data, the equivalent inertia of typical E-load devices is identified. Finally, the dynamic response and inertia of different load components under disturbance are compared and analyzed, and the relationship between the proportion of the E-load and the equivalent inertia of the composite load is also analyzed. The results show that the E-load has inertia, but the value is small. With the increase of the proportion of the E-load, the equivalent inertia of the composite load decreases.