Infrared temperature measurement technology is a commonly used technique for equipment fault detection in the power industry, which has significant applications in diagnosing faults for high-voltage substation equipment. To improve the accuracy of temperature measurement, an infrared temperature measurement model based on thermal radiation theory is established, and a comprehensive transmittance correction method is proposed. First, an infrared temperature measurement model is constructed based on the theory of thermal radiation, and this model is simplified according to practical application environments. Then, the influence of SF₆ gas transmittance on temperature measurement is taken into consideration, and corresponding transmittance correction method is developed to improve the accuracy of temperature measurement. Finally, practical temperature measurement experiments are conducted to verify the effectiveness of the established model and proposed transmittance correction method. The experimental results show that compared with the situation without transmittance correction, the accuracy of infrared temperature measurement is significantly improved after using the comprehensive transmittance correction method. The maximum reduction rate of measurement error before and after transmittance correction is 78.6%. This method lays a solid foundation for fault detection and monitoring of the power grid and shows broad application prospects for its safe operations.