The safe operation of surface power transmission system was influenced by many factors. Through exploring data， the influence factors on safety of this system were determined， which including four aspects of weather condition factor; operation and maintenance status of power transmission system; layout of transmission line; layout and management level of power transmission network cable. In order to get comprehensive evaluation of safety status of surface transmission system， comprehensive evaluation system of a mine was built. Comprehensive evaluation method of expert scores was chosen to get scores of safety status was 80.29 058. Based on segmentation criteria for each segment， it was clear that safety production of transmission system belonged to a good grade.