本文以机械传动中常见的开有花键或键槽的阶梯轴为例，根据刚度相同条件，推导出了在扭矩作用下阶梯轴所对应的当量长度的计算公式，从而可利用材料力学中求解等直径圆轴扭转刚度的一般公式简便地求出复杂形体轴的扭转刚度。 In this paper, the common spline or keyway stepped shaft in mechanical transmission is taken as an example. According to the same condition of rigidity, the equivalent length of the stepped shaft under the action of torque is deduced, which can be solved by using material mechanics The general formula for the torsion stiffness of a diameter circular shaft simply calculates the torsional stiffness of a complex figure shaft.