Abstract: For the simplification of anti-explosion design and evaluation processes of buildings, it is significant to calculate the equivalent dynamic loading for the buildings subjected to internal explosion. By means of hydrodynamic analysis method, the characteristics and distribution of the over-pressure on the surface of the structural members of a closed room subjected to central explosion were first studied. Based on the numerical results, the blast loading acting on the structures could be equivalent to be a bi-triangular uniform impulse, and the calculation method for this equivalent load was given, in which the influences of release area of the room were considered. Finally, by dimensional analysis and a series of numerical simulations, the empirical relationship between the equivalent load and the real explosion situation was obtained. The comparison between the simulated dynamic responses of the structures subjected to internal explosive and equivalent loading shows the validity of the equivalent method presented in this research.