中文摘要：

会计师事务所合并是否会导致审计市场集中度提高、竞争性降低，是监管部门在推动事务所通过合并实现“做大做强”时必须要考虑的问题。本文以事务所业务收入、上市公司客户的营业收入等作为计算基础，同时计算包含“四大”和剔除“四大”后的集中度指数和赫芬达尔指数，进而考察我国2005--2011年间整个注册会计师审计市场、上市公司年报审计服务市场集中度和竞争性的变化趋势，结果发现，本轮事务所合并使得我国本土大所的市场份额有显著提高，但我国审计市场基本仍属于竞争性市场，且本土所在大客户市场方面与“四大”仍有较大差距。对相关事务所合并前后市场份额的变化分析发现．并非所有的事务所在合并后市场份额都有显著上升。

英文摘要：

When promoting the CPA firms＇ mergers to make them ＂bigger and stronger＂, the regulator must consider whether the CPA firms＇ mergers will result in increased concentration and less competition of the audit market. What＇s the effect of CPA firm merger wave on audit market structure？ By calculating the CR and HI indexes respectively, based on the CPA firms＇ business revenue, their listed clients＇ total assets, sales revenue, etc., we examine the evolution of the concentration and competition of the whole audit market and the auditing market of listed companies＇ annual reports from 2005 to 2011. We find that large local CPA firms＇ market share has increased significantly, while Chinese audit market still belongs to the competitive market in general. We also find that there is still a large gap between the local CPA firms and the ＂big four＂ when it comes to the big customer. In addition, not all the firms＇ market share has experienced a significant increase after the merger.