In the existing method for analyzing the liquid tightness of the outer concrete tank in an emergency LNG spillage, the temperature variation over time inside the tank, and the concrete properties dependent on temperature and internal moisture content, have not been taken into account. In this study, the analyses for a typical LNG concrete tank subjected to thermal load due to spillage were performed with three different cases: the existing method was adopted in the first case, the transient temperature variation was considered in the second, and the temperature-moisture content dependent concrete properties were taken into account as well as the transient states of temperature in the third. The analysis results for deformation, compressive zone size, cracking, and stress of reinforcements were compared, and a discussion on the difference between the results obtained from the different analysis cases was made.