The application relates to a knapsack sprayer, which includes a mounting frame, a water pump, a power source, a medicine box, and a spray rod are arranged in the mounting frame, the mounting frame is also provided with a connecting piece, the connecting piece is provided with a switching plate, and the switching plate is provided with an elastic The sealing layer, the connecting piece is provided with an installation cavity, the switching plate is provided with an abutment piece, the inner wall of the installation cavity is provided with a hydraulic channel, the inner wall of the hydraulic channel is provided with an abutment piston, the abutment piston is connected with an abutment block, the inner wall of the installation cavity There is an annular groove, and an annular piston is arranged in the annular groove. The switching plate is fixed with a rotating handle for personnel to rotate. The rotating handle is provided with a limit piece, and the connecting piece is provided with a limit groove. pieces. By setting the connecting piece and the switching plate, the personnel can turn the switching plate to make the spray rod have the ability to absorb the liquid medicine, which is convenient for personnel to replenish the liquid medicine for the sprayer; by setting the water inlet port, the water intake of the spray rod can be increased, and the spraying effect of the spraying machine can be improved. The water replenishment efficiency of the machine.