On the basis of literature of social network theory and virtual team, this paper identifies the characters of human relation network, which are network structure (sparseness and centrality) and diversity of knowledge and constructs four hypotheses impacting the performance of employee in virtual teams. An empirical study on performance problem in Magic Program Team of NTT DOCOMO in Japan is undertaken and the hypotheses are validated. The result shows that both the network structure and diversity of knowledge have positive influence on employee performance. This paper provides reference for managing employee performance of virtual teams in hightech industries.