曲面上点的主曲率计算是确定轮齿啮合压痕平面投影形状的关键。文章摈弃通常运用啮合原理和坐标变换计算的思路，从曲面本身的性质出发，把幺正活动标架和外微分引入主曲率计算，得到简明、有效的主曲率计算的新算法，并结合压痕公式给出了一个应用实例。该算法可以推广到任意曲面的主曲率计算。

the calculation of contacted points´ principal curvature is the key to determine contacted area. Traditionally, the method of determining principal curvature is to make use of the theory of mesh and coordinate transform. However, this method is complex. In this paper, based on the feature of curve surface, moving frame and co-differential are employed to give a sententious, effective algorithm of principal curvature. Then, according to the formulation of contacted area, an application example is given. This algorithm can be used for calculation of principal curvature in all kinds of curve surfaces.