Abstract: Based on the ego-network perspective of social network theory, this study chooses the enterprise alliance data during 2009-2016 as the research sample. This paper explores the impact of network closure on enterprise innovation performance and analyses the mediating and moderating effects of knowledge flow and knowledge diversity. Results from negative binomial regression method show that: the network closure has an inverted U-shaped effect on enterprise innovation performance; knowledge flow plays a partial mediating role in the relationship between network closure and enterprise innovation performance; knowledge diversity could weak the inverted U-shaped relationship between the network closure and enterprise innovation performance.