With the development of internationalization in higher education, an increasing number of Sino-Foreign cooperative education institutes have been established in China over the last two decades. These institutes offer English-medium instruction where English is the working language for students to conduct various academic tasks. Based on a case study, this research examines how a group of freshmen enrolled in a Sino-Foreign cooperative education institute became socialized into the Community of Practice (CoP for short) in the institute and the factors that played into this process. It was found the students underwent differential levels of socialization into the CoP after one-year's study. While some students took an active part in the activities of the CoP and became more competent members of the community, some remained at the periphery of the community. The major factors that might have influenced the students' socialization include the English learning context of the participants before entering the institute, the participants' manipulation of resources in the institute, their engagement in the activities at the institute, their academic plans and self-image, as well as their English proficiency levels.