After the Executive Yuan passed “Bilingual Nation 2030”, many county(city) governments chose CLIL as the primary bilingual teaching model. This study constructed the practicable CLIL mathematics teaching model through the process of reflection and revision of the teaching action research. I designed two geometry units in angles and triangles, which were implemented in the fourth grade of elementary school from October 6 to 28, 110. I collected classroom observations, interviews, documents, personal journals and achievement tests in Chinese and English for comprehensive analysis. The following findings are presented: 1. CLIL learning contexts can provide Chinese according to students’ needs, integrate 70% of English into the classroom, and arrange heterogeneous groupings to promote peer communication and interaction. 2. Curriculum design can arrange hands-on activities and integrated literacy assignments with different levels of difficulty according to the subject content. 3. Teaching implementation can adjust the arrangement of mathematics textbook activities, integrate the same mathematical concepts, and plan by the CLIL content and language cycle. 4. Learning assessment focuses on English listening and speaking formative assessment in the classroom, and finally returns to the Chinese mathematics textbook exercises to check mathematical concepts. 5. All students’ performance in mathematics was stable and not affected by the CLIL instruction, but some students’ performance in mathematics was affected by their ability to read English words and sentences.