中文摘要：

本文基于2004年到2008年上市公司样本数据，研究股权分置改革的政策有效性。考虑到股权分置改革的分批逐步推进特性，本文运用双重差分方法进行分析。研究结果发现，股权分置改革显著改善了公司绩效，总资产收益率提高了2．19％，并且股改具有一定的持续效应，股改当年总资产收益率提高了1．14％，股改后第一年进一步提高1．69％，但第二年开始股改政策效应减弱，在第三年甚至变为显著为负的影响。本文的研究对于认识股权分置改革的有效性及其长期影响有重要意义。

英文摘要：

By using the data from 2004 to 2008, this paper studies the policy effect of stock market reform. Based on the characteristic of gradual stock market reform, we use the method of difference - in - difference to analyze the policy effect of stock market reform, and find out that stock market reform improves firm performance extensively, ROA improving by2.19% . Further more, the research finds out that this policy change has consistent impact： ROA improves by 1. 14% in the year of stock market reform and by 1.69% in the first year after stock market reform, and the impact of stock market reform decreases after that. This research is important to understand stock market reform.