Planetary carriers are the main components of planetary gearboxes. However，the current effective diagnosis methods of planetary carrier crack are limited. When the planetary gearbox is in operation，the planetary carrier crack will reduce the contact stiffness between the carrier and planetary bearing and also cause a small additional angular displacement of the planet gear closed to the crack. This paper introduces the influence of planetary carrier crack on the vibration signal of the planetary gearbox. Then a method based on amplitude and phase demodulation for planetary carrier crack fault is proposed，which is combined the synchronous average，vibration separation technique and narrowband demodulation. The angle domain synchronous average technique is used to eliminate the influence of the speed fluctuation and other rotating components. The angle domain synchronous average signal is reconstructed by vibration separation technique. The vibration separation signal is obtained by synchronous average. The amplitude and phase characteristics of the planetary carrier are obtained by narrowband demodulation. Characteristics of planetary carrier fault are extracted by observing changes in amplitude and phase plots. The analysis results of the planetary gear transmission testrig measured signal show that the method can effectively diagnose the planetary carrier crack failure.