To improve the response speed and robustness of the synchronous steering high clearance sprayer to the target attitude, a sliding mode active disturbance rejection controller was proposed to realize the attitude control for the synchronous steering chassis. Firstly, the attitude control model was built based on the synchronous steering structure. Then the attitude control model of the sprayer was decoupled and transformed into standard type of feedback system．After that, the extended state observer was designed to compensate the total disturbance of the model in real time, and the terminal sliding mode control rate was derived according to the attitude control model of the sprayer. Finally, the performance of the attitude controller was verified by simulation tests and field tests. In the field test, when the target angle was 5°, the response time of the front and rear steering angles of the sprayer was 1.55s and 1.45s. When the target angle was 20°, the response time of the front and rear steering angles of the sprayer was 3.05s and 2.95s, respectively. Compared with the traditional PID controller, the response speed of the forward and rear steering angles of the sliding mode active disturbance rejection controller proposed were increased by 8.42% and 1.89%, respectively, and the steady-state error was decreased by 2.96% and 3.15%, respectively. The simulation and field test results showed that the sliding mode active disturbance rejection attitude control algorithm had fast convergence speed and strong robustness, which can meet the needs of unmanned autonomous navigation operation of the sprayer in different environments.