Thermocouples have been widely applied in the measurement of temperature uniformity of vacuum furnaces. The effects of geometry and emissivity of thermocouple on the temperature uniformity measurement have not been sufficiently investigated. These effects have been investigated by numerical simulation method in this paper. The results show that the influence of diameter of thermocouple on the steady-state temperature of commonly used thermocouples is close to the influence of emissivity. The 0D model analysis shows that the sensitivity of thermocouple temperature to the relative change rate of diameter is equal to the sensitivity to the relative change rate of emissivity, which verifies the accuracy of the numerical simulation conclusions. This article provides a theoretical guidance and technical reference for temperature measurement of vacuum furnace.