Abstract. Operation Security of transmission line is affected by operating temperature of bare overhead conductors. IEEE Standard Model has reflected that the current of a conductor should be decreased when the temperature difference between the core and surface exceed the special value. In order to accurately estimate the operating risk of bare overhead conductors, a model is proposed to calculate core temperature of a conductor based on BP neural network in this paper. An experimental plate was designed to validate the proposed model under the free convection and forced convection condition. The experimental and calculated results are analyzed and discussed.