Insulated Gate Bipolar Transistor (IGBT) is the core component of current converter equipment in application scenarios such as flexible DC transmission and flexible AC transmission, and its junction temperature increases significantly with the increase of current level. Therefore, the junction temperature control of IGBT devices has become one of the bottlenecks to further increase the transmission capacity. Al/Diamond material has a much higher thermal conductivity than traditional packaging materials and a smaller coefficient of thermal expansion, so applying Al/Diamond material to IGBT packaging may improve the heat dissipation ability of IGBT and thus reduce the junction temperature. This paper constructs the IGBT model based on Al/Diamond material and the IGBT model based on traditional copper material through COMSOL simulation software, and compares the internal electro-thermal-stress distribution of the two models. In addition, this paper calculates the maximum and average values of temperature, maximum and average values of thermal stress and other parameters of each component inside the model according to the simulation data set. After comparison, it can comprehensively reflect the greater enhancement of heat dissipation capability of IGBT after applying Al/Diamond material to its encapsulation, which provides guidance for the subsequent research on the encapsulation optimization mechanism of high-power IGBT devices based on Al/Diamond material and the actual device fabrication.