Abstract: The paper proposed a design scheme of time-delay protection circuit for voltage-loss on the basis of analysis of large-scale power failure phenomenon of power supply and distribution system of underground coal mine due to transient voltage-loss, and introduced design idea and working principle of the circuit in details. The circuit uses double rectifier to charge capacitance and control constant discharge of capacitance. The practical application shows that the circuit has low design cost, is reliable and safe, can effectively solve existing issues of traditional high-voltage switch such as delay time is not controllable combining with time-delay protector and high-voltage integrated protector.