The formula of the curve tangent slope at some peculiar point in the orthograph on the stereoscopic surface intersecting line and the method of making tangent are given as well.

• 本文通过可展曲面的微分不变量,导出可展面的曲率线与曲率特征,并以锥面和切线曲面为例阐明这些特性的几何意义。