Abstract: In order to analyze potential hazard of LNG leaked to the ground, it is necessary to predict its diffusion and evaporation rate accurately. Based on dynamic model of liquid diffusion and heat transfer model, this paper uses a differential method to establish a prediction model of diffusion radius and evaporation rate. The model, changing with time and set under the condition of continuous LNG leakage, overcomes the limitation of 1D Fourier equation. According to the established forecast model, the evaporation rate of LNG liquid pool increases linearly with time before reaching maximum value, and then decreases with time, that is, inversely proportional to the square root of time. Taking the cylindrical 5 m³ LNG storage tank as an example, the calculation shows the leakage rate of LNG is 19.92 kg/s, it takes 69 sec to leak completely, 33 sec to reach the maximum radius of the liquid pool which is 7 m. Evaporation rate increases linearly to the maximum of 19.92 kg/s from 0 sec to 33 sec, is inversely proportional to the square root of time during 34 sec to 69 sec. During this period, thickness of the liquid pool increases gradually from 2.3 mm to 6 mm.