Driven by fierce global competition, flatter organizational structures, and the growing complexity of tasks, boundary spanning behavior is increasingly emphasized theoretically and practically, especially for externally dependent work teams. The current study aims at answering the questions of whether, when, and how an individual’s boundary spanning behavior impacts his or her task performance within the team. We surveyed 272 employees from 57 new product development teams in China to explore boundary spanning behavior by individual team members. Results indicated that informal leader emergence mediated the relationship between an individual’s boundary spanning behavior and his or her performance within a team. Moreover, cultural value at the team level plays important role in the above relationship. Group power distance positively moderated the association between boundary spanning behavior and informal leader emergence. An overall mediated moderation model of the interaction between boundary spanning behavior and group power distance on task performance via informal leadership emergence was confirmed. The implications of the research are discussed.