Abstract: The studies on stress, strain and pore pressure of mudstone during heating are significant in many fields, such as heave oil recovery, nuclear waste storage and civil engineering. The literature investigation indicates that rare related works have been done in this area and ongoing studies still stay in infancy all over the world. To our knowledge, few experiments and models have been revealed in domestic research activities. While some thermo-elasto-plastic constitutive models are successfully created by introducing temperature effect into the modified clay-based Cambridge model. Here, a thermo-elasto-plastic model for mudstone is proposed, which is capable to simulate change of stress, strain and pore pressure under in-situ boundary conditions. Furthermore, inner bed mudstone data of Xinjiang’s heavy oil field are applied in this model. Results of pore pressure and axial strain are obtained, and they agree with those of foreign experiments. By using the function for temperature field during steam chamber expansion of SAGD, constitutive failure of mudstone with different saturations is forecast. The results can effectively solve the problem that the inner bed mudstone hinders the steam chamber expansion.