The vibration response of a planetary gearbox has a time-varying and non-stationarity due to the effect of planet gear passing, the rotation of sun gear and a planet carrier, and other time varying conditions. However, the traditional synchronous average cannot be directly applied to the planetary gearboxes. In the light of such problem, this paper proposes a fault feature extraction method based on foreign windowed synchronous ave raging, which is based on angle domain windowed synchronous average of envelope signal to overcome the ime-varying transmission path and non-stationarity . This method using spectral kurtosis to extract the envelope signal of the vibration signal of the planetary gearbox; Then, the enveloping signals are resampled by the calculation order tracking technique. The rotation of each carrier, the appropriate window function and window width are selected for windowed interception of angle domain signals. Finally, the gear meshing tooth sequence feature is verified, and the vibration separation signal is reconstructed by windowed signals according to rearranging tooth sequence, extraction of gear fault characteristicsby angle domain synchronous average of vibration separation signals. Fault analysis of planetary gearboxes measured signal shows that the method can effectively extract the planet gearbox fault characteristics.