With the going of the running time, the fault of the wind turbines happened frequently, which result in the long nonscheduled shutdown time and the great economic loss. The vibration signal of the wind turbine is acquired, processed and analyzed, which can provide the equipment performance report and the reasonable maintenance advice for the field staff. Therefore the field staff can make a reasonable maintenance plan and manage the equipment scientifically, which shortened the nonscheduled shutdown time and improved the availability of the wind turbines greatly. In the wind farm the rotator speed is low, the wind load is varied and the base is flexible, which is different from other field and result in the rotate speed and the vibration amplitude of the mechanical drive system is varied. The fault is determined with the same diagnosis standard, which results in the error warning and brings down the diagnosis accuracy greatly. The method of trend analysis based on working condition classifying is introduced, which can reduce the error warning of the wind turbines vibration-monitoring system effectively.