The composition and working principle of NK 7397 piston air compressor are briefly introduced， and the take-off fault of primary safety valve is analyzed in detail. Through analysis and research， it is found that the reasons for the take-off of the primary safety valve include the failure of the valve itself， the blockage of the downstream gas flow and so on. In view of these fault causes， the corresponding solutions and preventive measures are put forward， such as strengthening preventive maintenance， reasonable selection of maintenance strategy， reducing personnel errors， etc.， in order to reduce the equipment failure rate and ensure the normal operation of the compressor.