Abstract: Blasting vibration damages have serious threats on the safety and stability of existing constructions. However, the dynamic loading in millisecond delay blasting is very complicated. There must be significant differences from actual engineering conditions when adopting simple triangle or trapezoid dynamic loading to analyze such vibration problems. Based on the analysis of pressure changes, volume expansion, fracture developments and gas motions in the blasting holes, an accuracy model of blasting loading over time was proposed. Also, for the far field vibration, the dynamic loading of each blasting hole was satisfied by the unified theory and Saint Venant's theorem. Thus, the dynamic loading of each blasting hole equaled the uniformly distributed loading on its cutting surface. In this way, the millisecond delay blasting problem was transformed into an equivalent boundary problem. Finally, a numerical model was built by the FLAC3D software. The physics and mechanics parameters, the propagating and damping parameters, and the dynamic loading model were used to predict the peak velocity curves. Compared with the measured in-situ data, the accuracy of the simulation was verified and the safety criterion formulas were calculated with the predicted effective tensile stress curves.