Abstract: The occasional parking brake failure of EMU (electric multiple units) brings safety hazards of train sliding for EMU train parking on slopes. The working principles of parking brake control principle and DASV (dual acting solenoid valve) are expounded, and it is judged that the EMU parking brake failure is caused by stuck DASV. By disassembling and analyzing the solenoid value, it is further deduced that the valve stem (plunger) sealing element sliding until adjacent to copper sleeve vent is the cause of DASV stuck. The champer deburring technique adopted for copper sleeve vent makes it not smooth enough, causing the sealing element stuck when it reaches the neighboring area，finally leading to the DASV failure to apply the parking brake normally. Two improvement measures are proposed: to adopt grinding deburring technique for copper sleeve vent, replace the two K-shape sealing rings in stem middle to O-shape sealing rings, and adjust the stem local structure with the O-shape rings; quantify the lubricating grease used on the DASV stem sealing element. As for the improvement measure, DASV test samples are tailor-made, and the failure reproduction test is carried out after fatigue test, and test results verify their effectiveness.