With the continuous improvement of supply chain concentration, the motivation of enterprise managers to implement earnings management is gradually strengthened, which reduces the authenticity and comprehensiveness of earnings information, and finally leads to the decrease of earnings transparency. From the perspective of upstream suppliers and downstream customers, the earnings transparency by three indicators: earnings aggressiveness, earnings smoothing and transparency composite index is measured. Based on the data of 6104 supplier concentration and 7654 customer concentration of Listed Companies in Shanghai and Shenzhen A-share manufacturing industry from 2010 to 2017, the mechanism and impact of supply chain concentration on earnings transparency are studied . The results show that: ①As for the whole supply chain, the enterprises with high concentration of supply chain have strong motivation to artificially inflate and smooth earnings, which has a significant negative impact on the transparency of surplus, and the motivation to artificially inflate earnings is higher than that to smooth earnings; ②Enterprises with a high degree of supply chain concentration have a stronger motivation to inflate their earnings than to smooth them; ③After distinguishing the property rights, the first two conclusions are still valid, but they are more significant in non-state-owned enterprises. In addition, it is found that the earnings transparency of enterprises is not affected by their size, while the higher operating risk will enhance the motivation of the management to inflate earnings and smooth earnings, which will reduce the earnings transparency of enterprises.