In order to analyze potential risk in LNG leakage on the ground, it is necessary to predict accurately spread and evaporation rate of LNG pool. Used are dynamical model and heat transfer model of liquid diffusion and applied is the differential method to predict the spreading radius and evaporation rate changes of liquid pool along with time. Results show that liquid pool evaporation rate will rise linearly up to the maximum value along with time and then drop inversely proportional to the square root of time. Accurately calculated are changes of leakage and evaporation rate and spread radius change of the liquid pool as well as changes of cryogenic liquid quality in dike and liquid pool thickness in actual leakage accident, which is useful reference for LNG leakage risk assessment, emergency response and personnel evacuation in case of leakage accident.