正投影法是绘制工程图样的基本理论。正投影图是反映工程形体的最主要的一种图样，因此，快速、合理地运用一定的读图方法将一二维平面图形转化为三维形体，也就是读懂正投影图，了解图样所表达的设计意图，是每位工程技术人员必须具备的一项基本技能。文中就阅读正投影图常用的3种方法——形体分析法、线面分析法、方箱法进行了阐述，以期对教师的教学有一定的参考价值。

Orthography is a basic theory for drawing the “engineering drawing”, and orthographic drawing is the major design to show engineering objects. Turnning the 2D graph into the 3D one quickly and rationally by using certain reading methods is a basic skill for every engineers and technicians, and it is an effective tool for them to understand the design intention. Three methods for reading orthographic drawing were proposed in the paper to provide a reference for teachers, which were analytical method of shape, analytical method of line and plane, and boxing method.