The static equivalent wind load provided by the Chinese Load Code is equal to the inertial wind force called “inertial wind load (IWL)” method, which can produce the same first mode displacement response as the actual value, but cannot exactly produce other responses, especially the base shear force. The structure total dynamic responses (including background response and resonant response) are evaluated by IWL method and method of random vibration theory, respectively, and then accuracy factor of the IWL method, C, is defined as the ratio of the two kinds of total dynamic responses. Study on the factor C show: ①when the first mode of the structure is bending style, the accuracy factors of the base shear force are not less than 95% to almost steel structures and some reinforced concrete (RC) structures whose first natural frequency is not more than 0.29Hz; ②when the first mode is shear style, the accuracy factors of the base shear force are not less than 95% to some steel structures whose first natural frequency is not more than 0.7Hz; but the accuracy factors of the base shear force are less than 95% to all of RC structures; ③when accuracy of the responses produced by IWL method is too low to meet the engineering requirements, the response values must be corrected and a method is suggested.