Concrete Structures principle is a major important professional basic course of civil engineering, and is a bridge of mechanics and subsequent courses. Features of the course are more concepts and formulas. Especially, the formulas of normal section bearing capacity calculation that is the core content of this course have more types. The students are afraid of difficulties if they have no good way to learn various formulas completely by rote, thus they do not learn good the core content. So this article focuses on teaching them to fishing way to build all kinds of normal section bearing capacity calculation diagram by expanding space imagination, then the corresponding formula is derived by means of mechanical equilibrium knowledge. The students do learn by analogy and better learn the part core content.