A new type residual current protector is designed in this paper. Using residual magnetic flux and the resonance voltage as leakage current signal in iron core, when there are residual current in power suply system, the device can automatically take relevant actions according to the real-time residual current value that is detected by detection circuit. The protector can be used to against electric shock and protect a ground fault. When the protection is occurred, the residual current protective device (RCD) possesses the inverse time lag function, ideal time delay and the automatic reclosing function. It also transmits the fault information to control center by the inter-integrated circuit (I2C) bus. Resonant circuit can avoid live parts injury, which limit the current value through contact resistance, and does not interrupt the work of electrical equipment. So the RCD can be used in all kinds of low voltage single-phase system that will snsure the safety and the reliability of the power supply.