The invention provides an autonomous flight pesticide spraying unmanned aerial vehicle controlled precisely and a plant protection method using the autonomous flight pesticide spraying unmanned aerialvehicle controlled precisely. The autonomous flight pesticide spraying unmanned aerial vehicle comprises a fuselage, four or more rotor wings, an undercarriage, a mounting plate, an externally-hung pesticide box, a control device and a power source. The control device of the unmanned aerial vehicle collects environment data in real time, and comprehensive dynamic adjustment is conducted accordingto the environment data, specifically, the expansion amount of expansion joints is adjusted according to the deviation angle, a wind speed empirical value is added on the basis of the expansion amount, and thus spraying precision is improved; and PWM is adjusted according to the wind speed, the spraying amount is increased, and the unmanned aerial vehicle plans a path automatically and makes a return flight automatically under the situation that the wind speed is too large. According to the autonomous flight pesticide spraying unmanned aerial vehicle controlled precisely, the spraying precision can be effectively improved, and the using safety of the unmanned aerial vehicle is improved.