With the tide of globalization, the external environment that schools face turns uncertain and complex. In response to the new challenges, teacher teams need to manage boundaries to maintain the sustainable development. The two studies reported in this paper, aimed to examine the boundary activities of teacher teams of middle schools in China. In order to achieve the research objective, the first study employed an inductive approach to identify a set of boundary activities that teacher teams engage in to manage the relationships with the outside. In the second study, the exploratory factor analysis and confirmatory factor analysis were conducted to build a valid and reliable scale for the boundary activities of teacher teams. Data from 332 teachers of 72 subject-based "teaching study" teams in 12 middle schools indicate a four-factor model of teacher team boundary activities includes the following subscales: scouting activities; task-coordinating activities; information filtering activities; and emotion cultivating activities. Similarities and differences between the current findings and existing literature have been discussed.