By using geometry analysis method,this paper educed calculation formula of normal direction gear side clearance when internal gearing involute gear transmission center distance waned slightly.

• 通过几何分析的方法,导出了内啮合渐开线齿轮传动中心距略变小时,法向齿侧间隙的计算公式,供齿轮传动设计计算之用。