Through the research of numerical simulation on the flow field characteristics of an aeroengine test between the inlet, the flow characteristics of the flow field between the engine test, analyzes the error of flow measurement with the measuring section and probes into position changes, then according to the specific section and deep position, and studied the boundary layer thickness changes with different Maher numbers and different Reynolds number, finally make a systematic analysis on the flow coefficient measurement method in engineering. The results show that the boundary layer is thinner and thinner, and the pressure measuring point is more and more distributed to the central area, and the measuring speed is more and more close to the average velocity of the section when the measurement section moves toward the engine inlet. The Maher number has little effect on the flow coefficient and the flow coefficient increases with the increase of Reynolds number.