Big ideas refer to the core concepts and discourse patterns that can connect and organize fragmented knowledge. This article investigates and explores teachers’ comprehension of big ideas and the challenges for applying big ideas in second language (L2) classrooms among junior high school in Jiangsu Province. The findings are as follows: (1) Teachers mainly learn about big ideas through teaching research activities, expert lectures, and open classes, but most of them understand them at a superficial level. (2) The main influencing factors of teachers' big idea construction include insufficient teaching resources, limited time and energy, inadequate methodological guidance, and heavy teaching pressure. They expect to improve their ability to construct big ideas by receiving teaching resources, teaching methods, teaching experience, and teaching theories. (3) There are significant differences among teachers in southern Jiangsu, central Jiangsu and northern Jiangsu in terms of their cognitive level of big ideas, their ability to construct and apply big ideas. However, they all urgently need teaching cases, theoretical guidance, teaching discussions, and training. Pedagogical implications are provided for English teacher education on the construction of big ideas in L2 classrooms.