Abstract: In order to adapt to the short take-off and landing requirement under the condition of strong side wind, the large general-purpose aircraft should still have good transverse heading stability at large side slip angle. In this paper, the transverse heading characteristics of a large general-purpose transport aircraft were studied, it is found that there is a turning phenomenon in the transverse heading heading test date of the aircraft. And the measures to improve the transverse heading stability of the general aircraft based on spoiler were studied by means of the wind tunnel test and theoretical analysis. The results show that the root cause of the turning phenomenon of the data is the local separation of the wing, that as the strong upwash caused by the fuselage with side slip angle greatly increases the local angle of the attack of the center wing on the windward side, local separation occurs when the local angle of attack of the center wing on the windward side exceeds the stall angle of attack of the model airfoil. The installation of a spoiler on the side of the fuselage interferes with the flow of the upwash air, and as a result the advance separation of the airflow on the upper surface of the wing is restrained, the turning phenomenon of the transverse heading characteristic curve is eliminated, and the lateral heading stability of the aircraft is improved.