The invention discloses a metal tool box structure and a forming method thereof. The forming method comprises the following steps: integrally forming a rough seat body blank and a rough cover body blank with corresponding shapes and circular arc angles by proper metal plates in a drawing mode respectively, removing the residual materials around the rough seat body blank and the rough cover body blank in a mode of stamping and shearing respectively, and trimming and flattening circular arc sections and linear sections at opening end edges of the rough seat body blank and the rough cover body blank respectively, wherein in a seat body, the circular arc section and the linear section at the top of a lateral plate are inwards bent in a mode of stamping and bending respectively to form inwards bent flanges at the top of the lateral plate, the seat body and a cover body are assembled and connected by a hinge device, and the inner edge of the cover body is sleeved with the flange of the seat body during covering. Therefore, the strength and the durability of the tool box are increased; not only the seat body and the cover body are accurately aligned, but also the appearance of the tool box is flattened; and the service life and the appearance esthetics are greatly promoted.