In order to calculate the radial temperature distribution of overhead transmission lines accurately，it is necessary to determine the current distribution firstly in alternating field． In this paper，the self-inductance and mutual inductance of the conductor in the overhead conductor WEＲE deduced，and the current phasor value of each conductor was obtained on the basis of the structural characteristics of ACSＲ ( Aluminium Conductor Steel Ｒeinforced) and the coupling law between composite conductor fluxes． The average error we got was 3. 56% in comparison with numeraicl results． To get the cross-section temperature，we put heat generation rate on the finite element model． The accuracy of the method was verified by strict experiments in accordance with which the influence of the radial temperature distribution on the calculation of the current carrying capacity was analyzed，which provided a reference for dynamic rating of overhead lines．