A clamping tool having an adjusting device, which comprises a work head consisting of a left and a right clamps, an upper and a lower cover plates, a positioning shaft and push-in type dies with U-shaped notches, and a clamp handle, wherein the positioning shaft of the work head is arranged at the corresponding middle position between the left and the right clamps connected with the left and the right clamps through the upper and the lower cover plate via rivets, the push-in type dies with U-shaped notches are respectively arranged in concave die cavities of the left and the right clamps and are firmly connected with each other with screws, the adjusting device is arranged between the work head and the handle and includes eccentric adjustment blocks and adjusting bolts, device holes matched with the adjusting device are arranged on the left and the right clamps, the eccentric adjustment blocks are respectively assembled in the device holes, and the left and the right handles are movably connected with the left and the right clamps through the adjusting bolts and fastening nuts. The utility model has the advantages of (1) simple structure design of the adjusting device for accurately adjusting the wear quantity of the work head due to long-time use of the clamp jaw and (2) simple operation, convenient use, reduced adjustment time of operators and improved work efficiency.