Abstract: The gearbox is a main transmission component of the wind turbine. Its fault may cause the longest downtime of the unit.Accurate fault diagnosis can effectively reduce unplanned downtime,increase power generation and improve the economic benefits of the wind farm. In this paper,a novel method of order analysis of wind turbine gearbox is demonstrated. The magnetic grid pulse signal is used as the trigger source for vibration signal acquisition,which can realize uniform angle sampling under variable working conditions.The order spectrum can be obtained by Fourier transforming the vibration signal in the angular domain. This kind of hardware-based order analysis can avoid the influence of speed changing when locating eigenvalues. In gearbox tests of the simulation system of wind turbine unit,results of the order spectrum analysis show that this method can accurately locate the stable characteristic order of the gearbox under variable speed operation,which provides a new way for fault diagnosis of large wind turbine gearboxes.