Differential geometry is the most difficult among optics, mechanics, fluid mechanics and differential geometry. According to relevant published materials, the contents of optics, mechanics and fluid mechanics are relatively simple and easier to understand. Differential geometry is a complex mathematical theory because it involves many mathematical operations. It is the most difficult subject to explore complex geometric problems from the basic concepts of mathematics and try to deduce geometric results from differential equations, which requires students to have a high mathematical foundation and operational ability.