Abstract: High-pressure emulsion leakage is the main fault of support hydraulic system,which has characteristics of multiple,uncertainty and concealment.Based on the fact that emulsion leakage will generate continuous ultrasonic signals,a detector of leakage failure for support hydraulic system is developed successfully,and the corresponding criterion is defined too.Field application shows that the instrument can detect and judge the leakage location and level of support hydraulic system quickly and accurately,which can improve the support quality and ensure the safe production in the working face.