Abstract: This paper presents a vaporization model of remnant propellant on the ground and a diffusion model of the poisonous gas for liquid hypergolic propellant launch vehicle explosion. The estimated mass of remnant propellant on the ground, the equivalent diameter of contaminated zone and the evaporation rate of N2O4 and UDMH are conducted for a N2O4/UDMH liquid propellant explosion respectively. The present models are applicable for predicting the vaporization (time) of remnant propellant on the ground and the contaminated range of poisonous gas for large scale liquid hypergolic propellant launch vehicle explosions. It provides an available evaluation method for safety measurement at the space vehicle launching site.