Abstract: The paper analyzed influence of complicated underground circumstance on leakage protector of DC trolley system of coal mine and problem of bad reliability that using single-chip microcomputer as controller of leakage protector,and proposed a design scheme that using PLC with good stability to instead single-chip microcomputer as controller of leakage protector.The paper introduced circuit principle and software design of leakage protector based on S7-200 PLC and indicated leakage protector based on S7-200 PLC existed problem of slow executive procedure of PLC,and proposed a scheme that using KDN-K3 as controller of leakage protector.It made field test of rapidity and stability for the leakage protector based on KDN-K3 PLC.The test result showed that the leakage protector meets with requires of rapidity and stability.