The operating temperature of sodium-sulfur battery cells is above 300°C for use in molten liquid state electrodes. In order to achieve this high operating temperature condition in a battery module composed of multiple cells, a thermal management system, such as an electric heater and insulation, is essential. The efficiency of the module is directly dependent upon the temperature uniformity inside the module and the heat dissipation from the casing. In the present study, a new numerical model for the thermal analysis of a sodium-sulfur battery module is suggested. The equivalent thermal properties of the cell are evaluated by detailed thermal analysis on the cell. The heat generation of the cell is modeled considering the electrochemical reaction process and the variation of the resistance of the battery. Using these equivalent thermal models of the cell, a zero dimensional lumped thermal model for examining the effects of insulation and heater operation is developed. Finally, the three-dimensional temperature distribution inside the battery module is predicted by solving the thermal energy conservation equation numerically. The distribution of temperature and the thermal energy efficiency of the battery module for various design variables, such as cell arrangement and heater operations, are summarized.