The classical model of liquid phase leakage can not accurately analyze the accident quantitatively. In this work, the leakage of LNG tank car is improved in combination with the ideal gas state equation, the change relationship between liquid level and pressure and between liquid level and time are explored, the relationship is introduced into the empirical formula, the change relationship between leakage rate and time is deduced, and the function expression is simulated. The results show that the leakage rate decreases exponentially with time. The dangerous concentration range of material leakage is calculated by combining the functional relationship with Gaussian diffusion. The error between the results and fluent model is within 26%. On the basis of modifying the traditional Gaussian model, the dynamic smoke diffusion model with time and pressure is obtained. The modified dangerous concentration range is used as the basic data to quantitatively analyze the mass of substances involved in explosion. The Thornton cone model is also used to explore the risk and influence range of fire and explosion by considering the flame jet angle, flame direction and environmental factors. The results show that jet fire, steam cloud explosion and boiling liquid expansion steam explosion cause death within 15, 15 and 298 m respectively. Compared with Aloha model, the overall error of the results is within 10.37%. It shows that the model is applicable to the theoretical calculation of LNG tank car leakage. The leakage at any time can be obtained by using the improved leakage model. Combined with the Gaussian diffusion of time factors, the dynamic diffusion process can be better described, and the calculated fire and explosion hazard range is more accurate, which provides a theoretical basis for emergency pre judgment, in-process response and crisis law analysis. It provides a scientific reference for taking flexible rescue measures in different injury areas.