Abstract: Graphite heater is the key component of the thermal conductivity measuring system of the pebble bed reactor core. Temperature field of the heater has a major influence to safety of the system and data accuracy. DTRM model, P1 model, ROSSELAND model and DO model were employed to simulate the temperature field of the graphite heater in the protection of vacuum environment. The method for calculating the temperature field of graphite heater was discussed and the influence of graphite thermal conductivity and surface emissivity on the temperature field was studied. Comparison results show that result obtained by DO model is most reasonable. The highest temperature of the heater drops as the thermal conductivity of graphite increases. When the thermal conductivity of graphite is less than 35 W/(m•K), the highest temperature is sensitive to graphite thermal conductivity. When the graphite thermal conductivity is greater than 35 W/(m•K), the highest temperature tends to be stable.