Submarine cable is a transmission component of high-voltage power, and the heat generated during the operation of submarine cable will cause the structural temperature rise and expand. Under the constraint of each layer, the submarine cable will produce large thermal stress and deformation, which will cause structural damage. In addition, the increase of temperature will lead to the decrease of elastic modulus of the polymer material inside the submarine cable, resulting in the change of mechanical properties of the submarine cable section. Therefore, it is necessary to study the stress and deformation caused by thermal expansion during the operation of submarine cables, and analyze the influence of temperature on the mechanical properties of submarine cables. In this paper, based on an offshore wind power project, a finite element model of submarine cable-soil was established in finite element software ABAQUS, and the temperature field distribution under steady-state current carrying capacity was obtained. Based on the results of temperature field, the thermal stress and thermal deformation of the submarine cable were calculated by the thermal-mechanical coupling method, and the change of mechanical properties of the submarine cable section under the action of temperature was analyzed. The results show that the highest temperature appears in the copper conductor during the operation of submarine cable, and the outer coating layer has the lowest temperature. With the copper conductor as the center, the temperature drop gradient along the inside radial direction is small, and the temperature drop gradient along the outside radial direction is large. The thermal stress is mainly concentrated in the metal structure, and the maximum deformation occurs in the steel wire armor. When the copper conductor and the optical fiber are located at the top of the cross section, the displacement is the largest, and the displacement is the smallest at the bottom. After considering the influence of temperature, the stress of copper conductor and optical fiber will increase, while the tensile and torsional stiffness of submarine cable will decrease, and the reduction of inverse torsional stiffness is greater than that of clockwise torsional stiffness.