As the agricultural unmanned aerial vehicle needs to fly close to the ground brings a need of the higher dynamic performance. In this paper, a cascade fractional-order PID control algorithm was proposed based on the traditional cascade integer-order PID control algorithm. In this paper,the Four-rotor UAV was modeled, and the parameters of the two algorithms were tuned by genetic algorithm. After obtained the optimal control, MATLAB/SimuLink was used to simulate and analyze.It was proved that the effect of cascade fractional order PID control was better than that of cascade integer order PID control.The experimental tests are carried out on the platform of a quadrotor UAV. The results show that the settling time of the cascade fractional-order PID controller shortened 0.24s than the settling time using traditional algorithm. Moreover, the new algorithm achieves a superior performance. The simulation results were verified.These results demonstrate that the cascade fractional-order PID control algorithm is suitable for the flight control of the agricultural unmanned aerial vehicle, and it is useful for the wide popularization and application of the agricultural unmanned aerial vehicle.