The main purpose of this article was to understand the current situation and challenges of the integration of mathematics and science (IMS) in Chinese primary schools. We used a questionnaire responded to by 453 primary school mathematics/science teachers and interviewed 7 teachers among them. Research showed that Chinese primary school teachers had a positive attitude toward IMS, but their beliefs about IMS were not high. Most teachers ever integrated mathematics/science in their class, but they did not have a complete understanding of the form of IMS in their minds. Results revealed that IMS in Chinese primary schools faced some challenges, such as teachers' incomplete perceptions of IMS, lack of resources, and insufficient school support and time. Finally, we proposed some recommendations for better implementation of IMS. This research would help policymakers, curriculum developers, educators, and primary teachers in China have an overall picture of IMS.