The increasing use of team as a basic operation unit of organizations makes team creativity a popular research topic. Team diversity is one of the most important factors of team creativity. the extant understanding of team diversity is focused on absolute distribution of diversity, while comparative distribution of diversity has rarely been studied. This paper proposes a new concept – the balance of team diversity, which is the comparative distribution of the team members' diverse characters. This concept helps to reveal the comparative strength of team diversity which is ignored by previous studies, and thus contributes to the research of relationship between team diversity and team creativity. This paper studies the effect of the balance of knowledge diversity and gender diversity on team creativity. We propose that the balance of team knowledge and gender diversity would positively affect team information elaboration and team creativity. Furthermore, team information elaboration mediates the relationship between the balance of team diversity and team creativity. We collected data from 80 teams, 451 students in Zhe Jiang Sci-Tech University via lab experiments. The task is designing the advertising video for Chinese government on World Expo. The experiment lasted one hour. Each team needs to put forward a video plan (between 200~500 words). Each team was made up of 4~7 persons and most of teams were made up of 6 persons. We designed a formula to calculate balance of team diversity. Team creativity was graded by three independent experts with scope from 1 to 10 (1 stands for least creative and 10 stands for most creative).Team information elaboration was measured with a scale of 4 questions developed by Kearney, Gebert and Voelpel (2009). The main results are summarized as follows: a) Balance of team knowledge diversity was positively related to team creativity, while the relationship between balance of team gender diversity and team creativity was not significant. b) Balance of team knowledge diversity was positively related to team information elaboration. c) Team information elaboration was a mediator of the relationship between balance of team knowledge diversity and team creativity. The theoretical implications are as follows: Firstly, we developed a new dimension of team composition -- balance of team diversity. It highlights comparative structural character of diverse team which is ignored by previous studies. Secondly, we found that team information elaboration is key mediating process between the balance of team diversity and team creativity. This paper also provided some theoretical guidance for managers to design a cross-function team or project team.