Since the independent directors quantity of listed companies in China has been required by CSRC in 2001，with the interlocking of independent directors，companies formed a closing network.We used the data of independent directors of China’s listed companies from 2003 to 2015，constructed the board network with the nodes of companies and ties of interlocking，then explored how centrality，structural holes and clustering coefficient affect the over investment level and how the external information resources quality moderate such influence mentioned above.We found that centrality and structural holes have a positive effect，while clustering coefficient has a negative effect and it will be more obvious when the quality of external information resources are lower.And the interactions of centrality，structural holes and clustering coefficient are not significant.Finally，we put policy suggestions based on the perspective of optimization of board network structure.