An impact tool head assembling mechanism is provided, including: an engaging sleeve, 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 which includes 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 a reference plane is defined as passing through the outermost peripheral edge and perpendicular to the axial direction, and an included angle between a line from the contact position to the outermost peripheral edge and the reference plane is between 25 and 65 degrees.