在初中物理范围内，关于透镜成像的作图，学生只能确定三条特殊入射光线的折射光线的方向．而对于任意入射光线的折射光线的方向如何确定，教材中没有给出这方面的知识．本文拟在初中范围内不借助课本以外的知识来解决这个问题．这样不仅可以丰富学生的知识，更重要的是能够培 In the physics of junior high school, students can only determine the direction of refracted ray of three special incident rays on the imaging of lens imaging. For the determination of the direction of the refracted ray of any incident light, the teaching material does not give this knowledge. This article is intended to solve this problem without using knowledge outside of textbooks in the middle school. This will not only enrich students’ knowledge, but more importantly,