In this study, a sociocultural perspective was adopted to understand the interplay between identity and agency in a context of science education reform in China. The manifestation of agency and the interaction between identity and agency were examined with two beginning science teachers when they teach with practical work at high school. As a feature of this study, the formation of the identity of beginning science teachers was conceived of as a site to locate and investigate teacher agency. Based on multiple sources of data, we have identified six spaces where the two participants’ agency was manifested: (1) personal characteristics; (2) personal beliefs; (3) interaction with students; (4) interaction with colleagues; (5) curriculum materials; and (6) high-stakes examinations. In each space, the two participants’ agency was contrasting in terms of perspectives and actions: one was passive, less confident and negative whilst the other was positive, more confident and positive. Moreover, it was found that their contrary actions had been caused by different perspectives. Based on the findings, a model of the interplay between identity and agency of an individual science teacher is proposed in a context of curriculum reform. The implications of this model for the future research and science teacher development are discussed in the last part of this paper.