Cabin pressure regulating system is an important system to ensure the safety of flight test. The oversize differential pressure often causes damage to the aircraft structure and seriously affects flight safety. The paper studies the flight test of cabin negative differential pressure relief. Firstly the basic principles and design feature of cabin pressure regulating system were introduced, then we analyzed and summarized the cabin negative differential pressure relief flight test including flight test method, refitting method, data processing method and safety evaluation, which can provide some guidances for the cabin negative differential pressure relief flight test of the civil aircraft.