Mathematics teachers' teaching beliefs play an important role in instructional practices and students' achievement. In China, transmissive teaching beliefs were prevalent before 2001. Since then, a student-centered concept has been advocated in the national curriculum reform; however, few studies have assessed contemporary Chinese mathematics teachers' teaching beliefs during the 20 years since the reform. In the current study, we elucidated the teaching beliefs Chinese teachers hold and their effects on instructional practices and students' mathematics achievement. A total of 1463 mathematics teachers and 12,437 students in grade 4 were recruited from Beijing, Shanghai, Jiangsu, and Zhejiang in Eastern China. Based on self-reported teaching beliefs using a short revised version of the Teacher Education and Development Study in Mathematics (TEDS-M), the study identified that contemporary Chinese teachers usually hold constructive teaching beliefs. In comparison, transmissive teaching beliefs showed significantly higher scores for teachers with more than 20 years of teaching experience. Moreover, male teachers and those with more teaching experience were more transmissive, but the effect of gender was small. The indirect effect of teachers' teaching beliefs on students' mathematics achievement through perceived constructive instructional practices was revealed using a multilevel structural equation model. This study illustrates the teaching beliefs of Chinese mathematics teachers and their effects, using evidence collected from a more general perspective.