Abstract: The characteristics of RC circuit in relay circuit of computer interlocking system is analyzed. Function of RC circuit in several typical relay circuits is expounded. By adding RC circuit, the fall of relay circuit can be delayed. By choosing appropriate value of voltage and resistance, requirement of relay sequential circuit can be satisfied. While increasing the delay time of the relay, RC circuit also exerts certain impact on the circuit stability. The overall structure of circuit must be considered with other factors such as relay standard status.