This study explores how physics teachers in a high school negotiate the relationships between individual and collective agencies in the context of the on-going curriculum reform in China. Drawing on Bandura's social cognitive theory, the study employs ethnographical methods including observation, interviewing, and the researcher's and teachers' reflective journaling through the researcher's involvement with various school activities. The findings indicate that collective teacher agency creates a platform for individual teachers' professional development, a conducive culture for teacher collaboration, and provides concrete examples that individual teachers can constantly refer to, reflect upon, and learn from for reform implementation. The results offer an understanding of the influences underlying physics teachers' agency deployment as they engage with curriculum reform processes, especially the negotiation between individual and collective agencies. The findings justify a case for preparing physics teachers on how to deploy both individual and collective agencies in the face of the complicated social structures and ultimately shed light on the desired curriculum decentralization in the Chinese school system.