Abstract: This research explores the impact of customer concentration (CC) on firm performance from the perspective of vertical supply chain, and further discusses the moderating effect of the coordinate interaction and competitive coercion between customers from the perspective of horizontal supply chain. Based on the data of Shanghai and Shenzhen A-share listed companies and their top five customers, the empirical results show an inverted U-shaped relationship between CC and firm performances, which is more pronounced in non-stateowned enterprises. Furthermore, we build a set of customer coupling coordination degree metrics from the perspective of major customers’ purchasing behavior, and find that the inverted U-shaped relationship between CC and firm performance is strengthened by customer coupling coordination degree. In other words, the improvement of customer coupling coordination degree will strengthen both the positive relationship between moderate concentration and firm performance and the negative relationship between over-concentration and firm performance. This paper deepens the research into the mechanism of how CC influences firm performance, and provides empirical evidence for explaining the impact of principal relationship in supply chain on firm performance from multiple perspectives.

Key words: customer concentration, coupling coordination degree, firm performance, inverted-U shape