The invention provides a quick-change lock and an agent applying machine specially for cotton by means of the quick-change lock. The quick-change lock comprises a connecting base, a movable pin, an elastic part and a tube sleeve; the connecting base is fixedly connected with the tube sleeve, the elastic part is arranged in the tube sleeve, and the movable pin penetrates the tube sleeve in the axial direction and extends into the connecting base; the end, away from the connecting base, of the elastic part is fixedly connected with the tube sleeve, and the end, close to the connecting base, of the elastic part is fixedly connected with the movable pin; the movable pin can move in the axial direction in the tube sleeve, and a spraying device is fixedly connected to the lower portion of a spraying cantilever through the quick-change lock; a connecting column is arranged on a branch device, the cross section of the connecting column is in the same shape and size as a running hole in the connecting base, multiple through holes are formed in the upper end of the connecting column, and the diameters of the through holes are equal to the diameter of the movable pin. The quick-change lock and the agent applying machine specially for the cotton by means of the quick-change lock have the advantages that installation is easy, operation is convenient, a spraying mechanism can be quickly changed, adjusting operation is easy and fast, the agent applying area is broad, the cost is low and the efficiency is high.