The invention belongs to the technical field of rotation machinery fault diagnosis, especially relates to a planetary gear case fault diagnosis method based on order complexity, and is specially applied to a fault diagnosis method of a wind power planetary gear case under a variable working condition. The method comprises the following steps: preprocessing vibration signals; dividing faults of a planetary gear train into two kinds; obtaining a fault feature parameter; analyzing the vibration signals under a variable working condition of a planetary gear case; and performing instance verification discovery. According to the invention, the influence of the variable working condition can be avoided by use of an order analysis method, and the Lempel-Ziv complexity of angle-domain signals after order analysis processing is more stationary than that of time-domain signals. According to the Lempel-Ziv complexity of the vibration angle-domain signals of the planetary gear case, local faults and distribution faults of planetary gears can be identified, through simulation and analysis of actual cases, the effectiveness of the method is verified, and at the same time, under the condition of lack of fault data, the complexity can also be taken as the feature parameter for determining whether there is a fault or not.