The purpose of this study is to examine the economic impact of the merger of audit firms of different types on the original clients. By observing the merger of large audit firms with different purposes of consolidation (the merger of KPMG and the merger of Deloitte), the merger of large audit firm with medium-sized audit firm (the merger of Ernst & Young) and medium-sized firms merged and became large firms (the merger of Crowe Horwath). Viewing whether the client's earnings quality and market value were in excess of the overall growth after the mergers of audit firms of different types. First, the merge of large audit firms will help to enhance the earnings quality of their customers,but KPMG didn't raised the market value of its customers.In addition,due to the international affiliate to the merger - Deloitte after the merger has significantly improved the customer's earnings quality, and overall, its help to enhance the market value of its customers. Second, The medium-sized audit firms merged into large audit firms didn’t improved the earnings quality of the customers' and the market value. Third, the merger of the medium-sized audit firms into the sixth largest audit firm has improved the profitability of the customers,but the empirical results are not significant. Futher, the market investors are optimistic about the value of their customers. The empirical results of this project aims to the field help gain more understanding of whether audit firm mergers benefit to the market value of the clients for regulators, investors and the community reference.