The invention discloses a braking device for a PTO of a tractor. The braking device for the PTO of the tractor is used for braking the power output end after power of the PTO of the tractor is cut off; a clutch used for switching the power transmitting state is arranged between the power output end and the power input end; and a braking friction pad is arranged on the outer side of the clutch andconnected with a braking driving mechanism for driving the braking friction pad to move in the radial direction so as to make contact with or get away from the surface of a clutch shell. The power output tail end of the PTO can be braked according to the requirements of the working situation, when the tractor stops advancing, machines such as a hanging plough stop working immediately, and manipulation is convenient.