Gas explosion in building structures often presents the characteristics of long duration, small peak overpressure and multiple pressure peaks. Based on the equivalent single-degree-of-freedom method, the numerical calculation method of structural dynamic response under gas explosion was derived by the matrix of load and resistance and its accuracy and validity was verified by comparing experimental data. The results show that:compared with the actual gas explosion, the simplified explosion load will underestimate structural vibration displacement due to ignoring the change of load rate, and the existence of damping will reduce this calculation error. The longer the load duration of the same peak value is, the larger the deformation energy acting on the structure will be, thus the maximum amplitude and residual deformation of structural vibration will increase. Both the initial velocity and displacement will increase the vibration deflection and residual deformation of the structure. The initial velocity is equivalent to the additional impulse load on the structure, while the initial displacement is equivalent to the external static load on the structure.