“Computation of Bridge Structures” is an important specialized course for senior students majoring in bridge engineering, which is of great significance to the cultivation of students' ability to solve complex engineering problems. Understanding boundary conditions has always been a key and difficult problem for finite element beginners. However, under the background of paying more and more attention to practice and ideological and political education, the class hours of professional theory courses have been greatly reduced, which makes the course have many challenges, such as fewer class hours, more content, students' lack of interest, weak mechanical foundation, and never learned the theory of finite element method. In order to help students to understand boundary conditions quickly and deeply, the teaching exploration of integration with “Structural Mechanics” is carried out based on the “Eighty Five Percent Rule” proposed in recent years for optimal learning. Four groups of questions are set up based on the construction drawing of an actual continuous beam bridge. The boundary conditions are combined with the known knowledge of kinematic analysis and rod, leading to four gradually deepened levels of understanding about boundary conditions. These explorations enable students to dialectically understand the classification of boundary conditions, the relationship between imposing (removing) constraints and rods, the relationship between boundary conditions and geometric models, and the meshing of the finite element model. Using the idea that not only all boundaries are "connections", but also all nodes (sections) are "connections", the supports and all kinds of connections in MIDAS/Civil are represented by chain bars. The relationship between six degrees of freedom constraint directions and six chain bars is given, which lays the foundation for the specific operation of applying boundary conditions in the software in the future. The teaching practice in the past five years shows that the problem-oriented teaching method of “Computation of Bridge Structures” based on the “Eighty Five Percent Rule” has a good effect, and students rarely make mistakes in confusing different types of boundary conditions in the subsequent computer modeling.