An impact tool head assembling mechanism is provided, including: an engaging sleeve, being disposed on a front end of an impact tool, including a tubular wall and at least one projection, the tubular wall defining an axial direction, the at least one projection being protrudingly and retractably disposed on an inner wall of the tubular wall; an impact tool head, including a rod body and a flange radially protruding from the rod body, the flange including an inclined surface facing toward the front end and an outermost peripheral edge, a contact position being defined as a position where the inclined surface contact with the at least one projection; wherein as viewed along the axial direction, a distance between the contact position and the outermost peripheral edge is larger than or equal to 0.5 mm.