By interpreting the relevant provisions of APU start performance in the airworthiness standard of military aircraft and the national military standard of auxiliary power unit, main test item and method of military aircraft APU’s start performance on-board ground test and flight test accord with the requirement of both airworthiness and performance test of military aircraft was proposed. Then the verification flight test was carried on with a military APU. The research indicates that the ground tests for military aircraft APU starting performance should include cold starts, restarts, and continuous starts under different environment conditions. Flight tests should cover cold starts, hot starts, and continuous starts during level flight, as well as starts under typical and severe flight conditions. The tests revealed that both cold and hot ground starts of the APU take longer as ambient temperature increases, with hot starts under high-altitude conditions requiring the most time. During flight, the duration of the self-acceleration phase in cold starts increases with altitude but is less affected by airspeed. In contrast, hot starts during flight do not exhibit a clear pattern with altitude variations.