Considering the wide-ranging, abstract, theoretical, and flexible contents of structural mechanics in civil engineering, a teaching method named "3W3E" is proposed by taking the modular knowledge units as clues. In "3W3E" teaching method, six modules of why, what, how, evolution, examples, and engineering are adopted, by which the significance, basic concepts, analysis procedures, historical developments, calculation training, and engineering applications of the knowledge point or approach are respectively introduced. The proposed method has the distinct characteristics of progressive levels, emphasized contents, and complementary functions. Taking force method as an example, this paper introduces the implementation process and teaching plan details of the "3W3E" teaching method. Practices show that the "3W3E" teaching method can improve the learning initiative of students so that the abstract knowledge can be well understood, and can help students to apply the problem-solving skills more proficiently and to widen their engineering cognition.