Vent panel mechanism, as a common provision, prevents the pressurization of the airplane from reaching the unsafe level if any door subject to pressurization is not fully closed，latched，and locked, which monitors the closed state of door system effectively and raises the safe reliability of the airplane. Cam and fourbar linkage are most often applied in vent panel mechanism. Based on successful design case, design cruces and principle for cam, fourbar linkage and vent panel mechanism are given, and calculative method for effective vent area is introduced as well.