Abstract: "Deep learning" is an educational concept of promoting students' in-depth understanding, knowledge application and creation. The unit teaching design in this perspective provides an important reference for teaching practice. Based on the theory of "promoting understanding through design", a goal-oriented and evaluation-first "reverse unit teaching design" model is constructed, the basic implementation path of "content reconstruction — factor analysis — goal setting — evaluation design — activity design — practice and reflection" is proposed, and its effect is tested with the radian system in Concepts of Trigonometric Function in senior high school mathematics for example. The results show that the teaching design model is helpful to open up a new path for improving the efficiency of unit teaching and promoting students' real in-depth learning.