In order to meet the application requirements of power cable security monitoring, a design method of distributed Optic Fiber Carrying Capacity and temperature security monitoring system with Raman distributed fiber temperature sensing technology as core is proposed. This system uses Raman distributed fiber temperature sensor to monitor the temperature, the carrying capacity and other running status of the power cable line in the power grid in a real-time, intelligent and all-around way. The experiment shows that, the system can supervise the conductor′s temperature and carrying capacity′s running status of 20 km long power cable, and calculating the conductor′s temperature and actual measurement with the maximum deviation less than 1 ℃ and the locating accuracy is 0.5 m. Using finite element calculation, the correspondence of cable temperature and cable carrying capacity were obtained, which coincide with the actual condition.