This paper describes the phenomenon of a certain type of aircraft stalling and shutdown when powered by an APU during ground simulation of air altitude during the functional testing task of the atmospheric data calculation system;introduces the phenomenon of this problem and conducts root cause analysis from the APU system structure, control system principle, fuel supply process and combustion mechanism of combustion chamber. The reason for the stalling and shutdown of the APU is determined: the APU was actually at ground altitude, but received an altitude in the air. During the fuel adjustment control process, the APU reduced the fuel supply to match the “thin” air at high altitude. At this time, the actual demand for fuel is higher than the supply. Due to insufficient fuel supply, the APU's speed decreased and triggered underspeed protection, resulting in the APU stalling and shutdown. At the same time, it analyzes the possible impact of this phenomenon on the APU and the aircraft. Based on the analysis results, the usage restrictions that need to be paid attention to in the future are formulated to avoid the phenomenon of APU stalling and shutdown due to the inconsistency between simulated altitude and actual ground altitude, reduce the possibility of damage to aircraft equipment, and improve the service life of APU.