Based on the relations of interlocking directorate among China listed corporations,we established an inter-firm network and analyzed the influences of institutional environment to its formation.We used marketization indexes as variables of formal institution,and trust and government relationship as variables of informal institution.The findings showed that formal and informal institutions have different effects on inter-firm networks.Informal institution has more effects on inter-firm network than formal institution.Furthermore,the effect of marketization indexes on inter-firm network is nonlinear.Non-state owned economy development is negative to network centrality,while product market development,intermediary and legal organization development are positive to network centrality.Meanwhile,government relation and trust are all positive to network centrality.All these results indicated that informal institution factors,such as trust and government relationships,have played important roles to inter-firm networks formation and development in transition economy,while the formal institution factors mainly relying on price systems has weak impact on inter-firm network relationships.