Abstract: Aiming at the problems of cumbersome insulation detection and difficult fault location for medium and low voltage dry load,a dry load fault detection and location system based on S7-200 SMART is designed in the paper. The test circuit is controlled by PLC,and PID control principle is used to calculate the loop electrical parameters. The load fault can be judged and the fault point can be located by comparing the calculated value with the normal value. The test results show that the system can measure the insulation and resistance of each circuit in 100 s,and quickly locate the fault circuit,which verifies the practicability and feasibility of the system.