The perturbation method for estimating the the existing power system’s moment of inertia has poor applicability, while the statistical method can neither accurately account for the proportion of renewable energy capacity nor carefully consider the equivalent inertia of the load side. Based on the analysis of the equivalent inertia estimation principle of a synchronous generator, wind power and load side motor, a practical and fast estimation method of regional power grid moment of inertia based on statistical method is proposed. The proposed method does not need the system operation parameter data after disturbance, but obtains the overall inertia of the regional power grid by accumulating the equivalent inertia of the on-line generators and motors on both sides of the source and load. It also takes the influence of the renewable energy capacity proportion into account by using the regression fitting coefficient of historical data. Thus it has the advantages of strong robustness and fast calculation. Examining two actual frequency fluctuation accident scenarios of a regional power grid, the proposed method is used to estimate the regional grid inertia, and the accuracy and practicability of the algorithm are verified based on the results of the perturbation method.