1. A method for monitoring performance of an aircraft auxiliary power unit APU lubricant cooler, comprising: acquiring APU messages within a time period; obtaining the operation parameters of the APU lubricant cooler according to the APU messages, the operation parameters including lubricant temperature OTA and load compressor inlet temperature LCIT; obtaining a revised lubricant temperature OT by: revised lubricant temperature OT=lubricant temperature OTAâˆ’load compressor inlet temperature LCIT; and determining whether the performance of the APU lubricant cooler is in stable phase, decline phase or malfunction phase according to change trend of the revised lubricant temperature OT with respect to time, the determining comprising: in response to the change trend is less than a threshold value of decline, determining the performance of the APU lubricant cooler is in stable phase; in response to the change trend is greater than the threshold value of decline and less than a threshold value of malfunction, determining the performance of the APU lubricant cooler is in decline phase; and in response to the change trend is greater than the threshold value of malfunction, determining the performance of the APU lubricant cooler is in malfunction phase; and determining stable change trend of the revised lubricant temperature OT with respect to time when the APU lubricant cooler is in stable phase; wherein, the threshold value of the decline phase is around 1.5-2.5 times than the stable change trend, and the threshold value of malfunction is around 5-7 times than the stable change trend.