A kind of electric leakage alarm device was designed.Theoretical analysis on the operational principle of the electric leakage alarm device is mad in this paper.Experimental study on the electric leakage alarm device was carried out.The results showed that this electric leakage alarm device can not act while power-supply circuit works naturally,but once electric single-phase leakage occurs it can alarm as well as safeguards power supply and assure the reliability of power supply,it can be widely used in coal mines.