The invention discloses a tool head and method for controlling the buckling deformation in a thin plate die-free gradual edge turning process. A long cylindrical body is arranged at the upper end of the tool head. The lower end of the long cylindrical body is connected with a disc. The bottom face of the disc is connected with a big-end-down circular truncated cone. The diameter of the small end of the circular truncated cone is smaller than that of the disc. The large end of the circular truncated end is connected with a large cylindrical body, wherein the diameter of the large end of the circular truncated end is the same as the diameter of the large cylindrical body. The method includes the following steps that an inclined face of the circular truncated cone of the tool head makes contact with the edge of a plate material, and a gap of 2 mm to 3 mm is formed between the bottom face of the disc and the upper surface of the plate material; the tool head horizontally extrudes the edge of the plate material to make the plate material bent upwards till the plate material makes contact with the bottom face of the disc; the tool head moves along the periphery of the plate material so that the same deformation can happen to an edge to be turned; the tool head is lifted, the steps are repeatedly executed, and performing is completed; the edge to be preformed is shaped through the side wall of the large cylindrical body of the tool head, and a vertical turned edge is obtained. The tool head and method have the advantages that deformation of the plate material is controlled through the combination of the tool head and a program, the longitudinal upwarp in the die-free gradual edge turning forming process can be eliminated, and the tool head and method are easy to obtain and implement and feasible.