With the injection molding machine hydraulic system in the direction of high pressure, pilot-relief valve is widely used in injection molding machine hydraulic system control circuit. In practice, in order to maximize its effectiveness, protect the control system, accurate and timely diagnosis, troubleshooting pilot relief valve is a key part. Pilot-type relief valve failure will result in injection molding machine can not move. According to the phenomenon, the analysis of the reasons: the pilot valve spool spring break; Yin Ni hole plug; pilot valve port seal bad; the main spool stuck and so on. The corresponding precautions are as follows: replace or flatten the pad at the breakage for emergency use; clean and clear; grind or break the oil path for emergency use; grinding and cleaning. Pressure-limiting instability: Pilot-based pressure relief valve relief valve instability, manifested as low or high pressure hydraulic system, hydraulic actuator weakness or tubing, pump body, body burst. The reasons for this failure are: improper pressure adjustment; pilot valve spool spring bent or softened; oil is too dirty or poor fluid flow. The corresponding exclusion measures are: readjustment, correction, matting or replacement; replacement, cleaning. Pilot-type relief valve pressure limiting instability is a progressive failure, pilot-relief valve failure is a sudden failure, after the exclusion of the fault, the injection molding machine system should be limited by the pressure on the pilot-operated relief valve control Press again to adjust.