股份回购是指上市公司通过公开市场操作等方式，以现金的形式从股东手中购回已经发行的股票，用来留作库存股或者注销的行为。股份回购和股利政策一起，是上市公司支付手段的重要组成部分，也是资本市场的重要制度之一。大量的理论和实证研究表明，股份回购被广泛用于稳定股价、提高投资者信心等目的。随着我国资本市场的日益成熟，越来越多的上市公司将股份回购看作为重要的资本运作工具，回购活动的频率和规模显著提升。深入认识上市公司的股份回购行为，是规范发展资本市场的过程中不可或缺的一环。本研究在回顾了前人研究和我国股份回购制度发展历程的基础上，探讨了上市公司股份回购的动机与对股票市场的影响，旨在丰富这一领域的研究，并为相关政策的制定提供理论支持。首先，本研究从委托代理的角度讨论了上市公司股权激励计划对股份回购决策的影响。研究发现，上市公司实施股权激励存在一定的委托代理问题，被激励对象更有可能通过推动公司股份回购的方式获利。这种现象在公司治理更差的公司表现更显著，且这类回购有更高的股份回购下限，但公告后的市场表现更差。在附录中，本研究对美的集团和格力电器在股份回购中可能存在的其他委托代理问题进行了案例分析，并发现企业性质和股权结构会影响公司通过股份回购获利的方式。以上研究表明，在公司层面存在利用股份回购进行价格操纵的现象。其次，本研究讨论了股份回购对股票市场的定价效率和股价信息含量的影响。研究发现，我国股票市场的公开市场股份回购行为降低了股票市场的定价效率和股价信息含量，与西方学者的研究结果相反。进一步研究发现，上市公司股份回购中潜在的价格操纵行为不是导致定价效率降低的原因。通过对市场上投资者情绪的检验，本研究发现是我国的个人投资者带来的非理性交易阻碍了信息有效并入到价格中的过程，从而降低了股票市场的定价效率。最后，本研究考察了上市公司股份回购后的长期市场效应。研究发现，上市公司股份回购后24个月存在累计超过10%的长期超额回报。进一步研究发现，回购前收益率为负、不可做空、高市场情绪、低投资者关注、低机构持股率和低分析师关注的上市公司股份回购后的长期超额收益率更高。通过对长期市场效应的异质性分析，本研究认为回购后长期超额收益率主要来源于公司被低估的错误定价。同时，本研究说明尽管股份回购可能存在一些价格操纵行为和非理性交易，但从总体和长期来看，股份回购对我国上市公司的企业价值增长有更多的正面促进作用。

Share repurchase refers to the act of a listed company repurchasing its issued shares, which may be held as treasury stock or cancelled, from shareholders through open market or other means, typically using cash. Share repurchases, along with dividend policies, are an important component of a listed company's payout strategy and are also a significant institutional arrangement in capital markets. A large body of theoretical and empirical research indicates that share repurchases are widely used for purposes such as stabilizing stock prices and boosting investor confidence.As China's capital markets mature, an increasing number of listed companies view share repurchases as an important capital operation tool, leading to a significant increase in the frequency and scale of repurchase activities. A thorough understanding of listed companies' share repurchase behavior is an indispensable part of regulating and developing capital markets. This study, based on a review of previous research and the development of China's share repurchase system, explores the motives behind listed companies' share repurchases and their impact on the stock market. The aim is to enrich research in this field and provide theoretical support for relevant policy-making.Firstly, this study discusses the influence of equity incentive plans on share repurchase decisions from an agency perspective. It is found that listed companies implementing equity incentives face certain agency problems, making it more likely for incentive recipients to profit by promoting the company's share repurchases. This phenomenon is more pronounced in companies with poorer corporate governance, and such repurchases have a higher minimum bar, but poorer post-announcement market performance. In the appendix, this study conducts a case analysis of potential other agency problems in the share repurchases of Midea Group and Gree Electric Appliances, and finds that the property nature and the ownership structure can affect how companies profit from share repurchases. The above research indicates that there is a phenomenon of using share repurchases for price manipulation at the company level.Secondly, this study discusses the impact of share repurchases on the pricing efficiency and information content of the stock market. It is found that open-market share repurchases in China's stock market reduce pricing efficiency and information content, contrary to the study of Western scholars. Further research finds that potential price manipulation in listed company share repurchases is not the reason for the decrease in pricing efficiency. By testing investor sentiment in the market, this study finds that compared to the West, the larger number of retail investors’ irrational trading in China's stock market impedes the process of information being effectively incorporated into prices, thereby reducing pricing efficiency.Finally, this study examines the long-term market effects of listed company share repurchases. It is found that there is a cumulative excess return of over 10% in the 24 months following listed company share repurchases. Further research finds that companies with negative pre-repurchase returns, non-shortable stocks, high market sentiment, low investor attention, low institutional ownership, and low analyst coverage have higher long-term excess returns after share repurchases. Through heterogeneous analysis of long-term market effects, this study believes that the main source of long-term excess returns after repurchases is the erroneous pricing of undervalued companies. At the same time, this study illustrates that although share repurchases may involve some price manipulation and irrational trading, overall, share repurchases in the long term have a more positive impact on the value growth of listed companies in China.