In order to get the radial temperature distribution of overhead transmission, taking LGJ240/30 mm² wire as an example, the control equations of the electromagnetic-thermal coupling field of radial section of overhead line are established and the electromagnetic field and the temperature distribution of the wire over cross section are calculated iteratively by using ANSYS. On the basis of calculation results, the regular pattern and cause of current density distribution and radial temperature distribution are discussed. Calculation results are verified by designing and establishing the indoor strong current experiment platform. The results show that in the case of natural convection, the average error of temperature of steel core, aluminum-layer temperature, and aluminum surface temperature is only 1.72%. The accuracy of the proposed model is compared with the experimental formula of radial temperature under natural convection combining IEEE Std 738-2012. The comparison shows that the calculation results considering the heat source distribution of skin effect and heat conduction in air gap has less error when computing conductor radial temperature. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015AA050201).