Aiming at the limitations of traditional nonlinear control methods, this paper studies the L1 adaptive method. Taking a scaled UAV in the laboratory as the research object, a lateral nonlinear control system of UAV Based on L1 adaptive is designed. The system is a two in two-out nonlinear control system. Firstly, the lateral and lateral nonlinear kinematic model of the drone is derived and transformed into a form that conforms to the L1 theory. Secondly, an L1 state observer, adaptive law, control law, and low-pass filter were designed based on the controlled object model, and low-pass filters and adaptive gain parameters were reasonably designed based on the characteristics of the controlled object. Finally, the L1 adaptive control structure was composed of four parts: the controlled object, state observer, adaptive law, control law, and low-pass filter. The L1 lateral nonlinear control system model was built using MATLAB/SIMULINK tools and simulation results were analyzed. From the simulation results, it can be seen that in the case of nonlinear uncertainty in the lateral direction, L1 adaptive control can effectively control both roll angle rate and yaw angle rate, ensuring fast adaptation while also having a certain degree of robustness; Further research directions were analyzed based on the simulation results of the sideslip angle.