Gear tooth profile modification can be featured to improve working stability of gear equipments, abate noise and vibration, enhance loading ability and prolong usage life of the gears. Fine forged spur bevel gear are formed with molds, so it is economical to modify the gears by means of modifying mold cavity. Whether the modified gears can be separated from the mold with easiness is proposed to be the basic criterion of gear tooth profile modification design. Near the big ends and tooth roots is mainly the area which affects demolding after modification. According to the modified gear configuration, mathematical model is built to calculate the demolding check at any modification points on the fine forged spur bevel gear profile. And a corresponding program is developed, which is the main tool for the gear tooth profile modification design, and practical calculation has carried out.