Abstract: In view of the problem that the mutual heat effect is not considered in the calculation of cable conductor temperature in IEC 60287 standard, this paper proposes a thermal circuit model which can accurately and quickly calculate the temperature of tunnel cable conductor based on the heat transfer theory and considering the influence of mutual thermal effect on heat dissipation coefficient. According to the cable material properties, installation mode, grouping position and environment, the model parameters are determined. Based on the model, the total heat dissipation coefficient formula for horizontal arrangement of 500 kV extra high voltage (EHV) large section cables is further proposed, and the applicable range of the formula is obtained. The conductor temperature is obtained by the iterative calculation of the total heat dissipation coefficient formula. The results of the model are compared with the results of IEC and verified by the finite element method (FEM) thermal-fluid field coupling simulation. Ii is shown that the error between the results of model calculation and FEM simulation is less than 2.5%. When the cable is in rated operation state, the conductor temperature based on IEC standard is relatively low and the deviation of single cable is negligible, thus it can be ignored; the maximum temperature difference of three-phase cable is up to 5 ℃ when the cable is touching trefoil formation; the maximum temperature difference is up to 6 ℃ when the cable is in horizontal arrangement, and it decreases with the increase of cable surface distance. When the cable surface distance is greater than 0.75 times of cable outer diameter, the mutual thermal effect can be ignored.