The invention discloses a special tool for replacing a clamping cylinder of a fast forging manipulator. The special tool comprises a bottom plate, a clamping cylinder supporting seat, a clamp rear endface supporting seat, a clamp bolt supporting seat and a clamping rod bolt supporting seat, wherein the clamping cylinder supporting seat, the clamp rear end face supporting seat, the clamp bolt supporting seat and the clamping rod bolt supporting seat are fixed to the bottom plate and sequentially arranged in the length direction of the bottom plate. In the disassembling and reassembling processof the clamping cylinder, the special tool is adopted to be matched with a travelling crane, the potential safety hazard caused to constructors due to the fact that an overweight clamp is fixed through a chain block is avoided, and the work of checking, replacing and the like of the clamping cylinder can be safely and conveniently implemented; compared with an existing clamping cylinder replacingmethod, a large amount of time for operating the chain block is shortened; in addition, the position of the special tool is fixed, a large amount of time for adjusting the mounting position can be shortened when the clamping cylinder is reassembled, manpower is saved, the maintenance time is shortened, and the operation efficiency is improved; and finally, the work of checking or replacing the clamp, a rotary speed reducer, a rotary bearing and other components can be achieved.