To solve the problem of lateral oscillation of small UAVs in high-speed flight,this paper analyzes all kinds of factors causing oscillation from the perspective of the principle of the flight control system, focuses on such factors as flight control parameters and system delay,and conducts simulation verification to determine the cause of the oscillation.By adopting the measures of adding an adjusting coefficient to flight control parameters and reducing the system delay in high-speed flight,the effectiveness of the improvements is verified by simulation and actual flight,and the problem of lateral oscillation is solved.