The invention discloses a spraying device of a pesticide spraying unmanned aerial vehicle. The spraying device comprises an unmanned aerial vehicle body and a pesticide spraying tank body mounted at the bottom of the unmanned aerial vehicle body. Sliding grooves are formed in the bottom end face of the unmanned aerial vehicle body in bilateral symmetry. A locking groove extending to the inner side is formed in each sliding groove. Guiding grooves are symmetrically formed in the top end face of the pesticide spraying tank body. A pesticide storage cavity is formed in the pesticide spraying tank body. A first cavity is formed in the part, above the pesticide storage cavity, of the pesticide spraying tank body. A first bevel wheel is arranged on the inner bottom wall of the first cavity. A stirring rotary shaft which extends downwards and penetrates through an inner wall body, between the first cavity and the pesticide storage cavity, of the pesticide spraying tank body is fixedly arranged at the bottom of the bevel wheel and is connected with the inner wall body of the pesticide spraying tank body in a rotating fit mode. The bottom extending section of the stirring rotary shaft extends into the pesticide storage cavity. A second bevel wheel is connected with the top of the right side of the first bevel wheel in an engaged mode. A second cavity is formed in the part, on the right side of the first cavity, of the pesticide spraying tank body. The spraying device is simple in structure and can achieve automatic rapid mounting operation, the mounting efficiency is improved, and the sprayed pesticide evenness is improved.