<p>In this paper, a high-precision decoupling attitude stabilization control method for an agricultural six-axis Unmanned Air Vehicle (UAV) with optimal robust Active Disturbance Rejection Control is proposed. Based on the analysis of the attitude dynamics model of the agricultural six-axis UAV, a multivariable mutual coupling system, the roll, pitch and yaw control systems are designed independently, respectively. The effects of external disturbances such as wind and air flow on the agricultural six-axis UAV, uncertainty due to mass variation, mass loss due to reagent and petrol consumption, etc., and mutual coupling are considered as total disturbance. The optimization problem is to set up to optimally guarantee the control performance and robust performance of the control system and solved under inequality constraints by the Particle Swarm Optimization-Difference Evolutionary (PSO-DE) hybrid intelligent algorithm. The simulation shows that the proposed method is effective, the coupling effect is fully suppressed and the stabilization accuracy is improved. The fixed platform test and field flight test have shown well the practical effectiveness of the proposed method.</p>