In order to reduce cracks in the lining concrete of spillway tunnel of Baihetan power station, we discuss the impacts of surrounding rock behavior and lining thickness on thermal stress of lining concrete. On this basis, we make reasonable criteria of temperature control and put forward economical and feasible measures. According to the structure and material properties of lining concrete of the spillway tunnel as well as boundary conditions, we carry out three-dimensional simulation on temperature field and stress field during the construction of lining by using ANSYS. Results show that the larger the thickness of lining concrete is, the higher the concrete temperature is, and the later the maximum temperature comes; moreover, the higher the strength of surrounding rock is, and the larger the thickness of lining concrete is, the higher induced tensile stress is, and the reverse is true. Both surrounding rock behavior and lining thickness have effects on the temperature and thermal stress of lining concrete, so it is necessary to determine lining thickness according to surrounding rock behavior to ensure lining concrete safety on resisting cracks.