PURPOSE: A method for detecting the performance of an APU(Auxiliary Power Unit) is provided to avoid unexpected repairing by checking airplanes at the right moment and to guarantee flight safety and service quality. CONSTITUTION: A method for detecting the performance of an APU(6000) is as follows. The APU obtains an exhaust temperature EGT, an air compressor inlet temperature LCIT, a starting time STA, a service time TSR, and an air bleed pressure PT(6100). The EGT-LCIT, STA, TSR, and PT are compared with their own threshold value(6200). Based on the results comparing the EGT-LCIT, STA, TSR, and PT with their own threshold, each specific gravity is determined(6300). The performance of the APU is determined by the results comparing the EGT-LCIT, STA, TSR, and PT with their own threshold(6400). [Reference numerals] (6100) Obtaining exhaust temperature EGT, air pressure device entrance temperature LCTT, start time STA, user time TSR, and air bleed pressure PT; (6200) Comparing EGT-LCTT, STA, TSR, and PT with respective threshold values; (6300) Assigning respective weights according to the comparison results of EGT-LCTT, STA, TSR, and PT with respective threshold value; (6400) Matching the comparison results of EGT-LCTT, STA, TSR, and PT with respective threshold value after considering the weights; (6510) Whether it is greater than a first predicted value; (6520) Good APU performance; (6610) Whether it is greater than a second predicted value; (6620) APU performance is normal; (6710) Whether it is greater than a third predicted value; (6720) APU performance has entered a deterioration period; (6800) APU performance has entered a failure period; (AA,BB,CC) Yes; (DD,EE,FF) No