The investigation and analysis of LPG spill mechanism are made and cargo spill models, source strength released from LPG vapor in land and at sea are probed too. According to the facts of spill condition, systematic analysis is made on the suitable dispersion models which are applied to different spill and environment conditions, and source strength calculation models of multiple spilled resource and environment are analyzed as well, so as to put forward a comprehensive and systematic primary solution for vapor dispersion simulation of LPG. For the sake of convenient application, a computer software for risk assessment of LPG carrier is developed which can provide great assistance to the decision-making of emergency response and reach the target of reducing the damage of the life, property and environment to the smallest degree.