Abstract: Through the flight test, the internal flow field distribution and the inlet distortion of the 2-D supersonic inlet with the auxiliary intake door at low speed are investigated. The results show that mixing of the auxiliary intake flow and the main flow in the inlet would produce a low total pressure area in the downstream area of the auxiliary intake door, causing the distortion to increase and the total pressure recovery to decrease. Besides, the auxiliary intake flow rate and the resulting distortion increase with the increase of the engine speed, decrease with the increase of the flight Mach number, and there is no significant difference when the flight altitude changes. Meanwhile, the range of the low total pressure area and the distortion produced by the auxiliary intake flow increase when the sideslip angle increases to the left and right, and there is no obvious difference when the attack angle changes. In addition, by analyzing the correlation between the change of the low total pressure area at the outlet section of the inlet and the flow coefficient of each test point, the operating range corresponding to the opening and closing status of the auxiliary intake door is determined.