In the face of fierce competition, firms hope to cope with competition by building alliances and forming alliance portfolios. However, the impact of alliance portfolio size on the performance of focal firm has not been consistent. Based on the transaction cost theory and resource dependence theory, this paper uses the data of Listed Companies in Shenzhen growth enterprise market to explore the relationship between alliance portfolio size and firm performance in the case of resource redundancy. By using the method of multiple hierarchical regression, this paper analyzes 1455 "enterprise year" alliance portfolio size data of 336 enterprises, and finds that the increase of alliance portfolio size has a significant negative impact on the performance of the focal firm, and the absorbed resource redundancy and unabsorbed resource redundancy play a negative moderating role between the alliance portfolio size and the performance of the foal firm, and it strengthens the negative impact of alliance portfolio size on the performance of focal firm.