With the construction machinery hydraulic system in the direction of high pressure and high pressure development, pilot relief valve is widely used in construction machinery 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. 1, the control failure, so that the host does not move the pilot relief valve failure, will cause the host 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. 2, pressure limiting instability pilot pressure relief valve pressure relief, manifested as low or high hydraulic system pressure, 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 instability is a progressive failure, and more appear in the reserve motorcycle more hours of construction machinery; pilot relief valve failure to sudden failure, appear more in the reserve motorcycle hours less engineering Mechanical. After troubleshooting, the pressure controlled by the pilot relief valve should be readjusted to the pressure limited by the system itself.