The development of modern power systems is accompanied by the problem of inertia deficit, and there is an urgent need to evaluate the system inertia level. Especially, the accurate estimation of load-side inertia level is extremely important. Based on comprehensive statistics, a load-side inertia estimation method is proposed. Starting from the inertia analysis of load-side base elements, the expressions for load-side inertia estimation under various operation modes are given based on the inertia modeling of basic load units; the uniform correction formula for load-side inertia estimation is given considering the hidden effect of behind-the-meter power supply on inertia estimation. The simulation analysis is carried out based on the IEEE9 bus standard system, and the results show that the proposed load-side inertia estimation method does not exceed 5%.