As a well-known dairy company in China, Yili officially completed the acquisition of infant formula goat milk powder head company Ausnutria Dairy in 2022. This acquisition has become the largest merger in the dairy industry in recent years. This paper analyzes the motivation and integration process of Yili’s merger and acquisition of Ausnutria Dairy, and uses event research method and accounting research method to measure the market performance and financial performance of the merger and acquisition, and on this basis, the effect of the merger and acquisition is systematically evaluated. The study found that after the merger, the market responded positively, shareholder wealth increased, and mergers and acquisitions had a positive impact on profitability, growth ability and solvency in addition to a slight reduction in Yili’s operating capacity. Finally, the research puts forward the enlightenment of enterprise merger and acquisition, and provides experience for enterprise horizontal merger and acquisition.