According to the general education program in Mathematics 2018, the ability to solve math problems is one of the 5 most important mathematical abilities. Mathematical problem-solving abilities include the capability to generalize. “Quantitative Relation in the Triangle” is an important program topic that can develop students’ generalization competence. In this paper, we apply the action process to train grade 10 students’ generalization capacity in teaching quantitative relations in the triangle, thereby developing students’ mathematical problem-solving competence.