Abstract: Abstract: based on the domestic accounting firm merges in Chinese securities market from 2006 to 2009, the paper analyzes the market reaction, and the effects of merges on audit quality and audit fee. The paper finds that accounting firm merges have not improved the audit quality. The audit fee charged by big accounting firms rose if the firms become the domestic top ten after merges , but the audit fee by small accounting firms have not changed significantly. The market reaction of merge is significantly positive. It indicates that the strategy of growing bigger and stronger encouraged by regulators has taken effect partly. On the other hand, the accounting firms should take steps to integrate the quality control and risk management, and regulators should supervise the quality of merges to help the accounting firms to achieve synergy effects.