Microwave ablation, as an emerging method for treating lung cancer, has been widely used because of its advantages, such as being less invasive and having fewer side effects compared with other therapies, such as surgery and chemotherapy. The key to microwave ablation is to destroy the tumor tissue while minimizing the damage caused to the surrounding healthy tissues. Based on the heat transfer model of porous media, a two-dimensional simulation model of a spherical tumor surrounded by healthy tissue is established in this paper. The effects of tumor diameter, tumor porosity, and microwave ablation power on the highest temperature, ablation area, and volume of the tumor tissue were studied by using the software COMOSL Multiphysics. The results show that the porous heat transfer model is more practical than the Pennes biological heat transfer model. The tumor diameter and the tumor porosity have a great influence on the maximum temperature, the ablation area and volume. In this study, a more realistic model of microwave ablation of lung tumors was established, and the ablation results were predicted accurately, which provided the basic reference data for the selection of clinical therapeutic parameters of microwave ablation of lung tumors. To a certain extent, it can ensure that the ablation area completely covers the tumor and reduces the risk of tumor recurrence, which is of great significance in the accurate treatment of pulmonary tumors by microwave ablation.