Abstract: The Al-Si alloy shell has wider and wider application in radar industry, and the reliability of the shell is required to be higher and higher. Especially in the design of microwave power module, besides mechanical stress, thermal stress is also an unignorable factor. In this paper, a high-power package shell is taken as an example to carried out the transient calculation of the stress distribution of the lug of the Al-Si shell under the condition of high power output by the thermal-structural multi-field coupling simulation to identify the failure risk of the lug. Experiments are also carried out. The simulation results are consistent with the experimental results. The lug structure is optimized by the orthogonal experiment method to meet the application and design requirements, which has a good guiding significance for subsequent engineering application.