Because the temperature of heat medium in thermal recovery wells is very high, and casing is heated during steam injection process, which has become the main reason of casing failure. Therefore, it is very important to analyze crack propagation and casing failure under thermal mechanical coupling. Three-dimensional finite element model is investigated; geometry model is constructed with native and parasolid method in ADINA. The casing is modeled by native method and strata are modeled by parasolid method, casing are subtracted and merged with strata by Boolean Operation. Gravity and displacement loads are defined in structure model, and temperature load in thermal model. In structural model, casing is treated as thermoplastic material, and strata are treated as hot isotropic material. In thermal model, all materials are treated as heat conduction material. Thermal-mechanical coupling is calculated with the thermo-mechanical coupled analysis solver in ADINA, and casing damage process is calculated. According to the calculating results, the mechanism of casing damage is analyzed.