Mathematical modeling plays an important role in improving students' interests and attitudes in reasoning, communicating and solving problems. In order to understand modeling in the popular mathematics textbooks for primary schools in China, this study developed a modeling framework for K-12 mathematics textbooks, and used content analysis method to analyze China's current textbooks of primary mathematics in grades 3 to 6. The results showed that the samples follow a gradual development principle in terms of "content level,""appearing location," and "representation mode," but the scientificity of model content level needs to be enhanced. In the four stages of modeling, the contents for cultivating students' high-order thinking ability need to be further enriched. It is also suggested that more mathematical background knowledge should be covered in future textbook compilations.