股票回购是公司购买自身已发行股票的公司理财行为，市场择时是公司股票回购的重要动机之一，指管理层根据市场整体和公司特质性回报把握公司股价低点进行回购，对海外资本市场的诸多研究已证明该现象的存在。长期以来，A股市场监管政策对择时动机的股票回购限制严格，自2018年回购新政后才显著放宽，市场环境差异使得国外研究结论不一定适用于A股市场。对此，本文基于A股上市公司2013年4月至2022年2月的实际回购交易，使用相对回购价格RRP衡量回购的整体择时效果，使用回购公司组合月度收益率PPR的超额收益率衡量回购的公司特质性择时效果，研究A股上市公司回购择时效果存在性、回购新政实施效果和影响机制。 结果表明，回购新政前A股上市公司回购能取得显著的整体择时效果，但无法取得公司特质性择时效果，回购择时缺少超额收益，与海外市场表现不同。2018年的回购新政显著改变了A股市场回购的环境，提升了A股上市公司回购择时效果。新政后，A股上市公司各窗口期的相对回购价格显著降低，整体择时效果提升，且可以取得公司特质性择时效果，获得超额收益。 本文尝试探究回购新政的作用机制。使用中介效应检验发现，融资约束是回购新政提升上市公司回购择时效果的机制之一。新政通过放宽回购资金渠道，降低公司回购中的融资约束，进而提升公司回购择时收益。进一步分析发现，回购新政的影响具有异质性，对融资约束较大的公司回购择时效果提升较为明显。 综上，本文得到三点核心结论。第一，原有的政策限制是导致A股市场回购择时效果不同于海外市场的重要原因，回购择时相关理论在A股适用。第二，回购新政使得A股上市公司回购择时效果提升，有助于增加上市公司和股东财富、维护公司市场价值，在托市稳市、推动市场价格发现方面具备积极作用。第三，在当前市场阶段，放宽融资渠道是回购新政推动公司回购发挥积极作用的有效措施，建议在市场低迷时期进一步推进和落实。

Stock repurchase is a financial decision of a company to buy back its own share from the marketplace. Market timing is an important motivation behind stock repurchases. It refers to the practice of repurchasing at low prices on managerial timing of firms’ idiosyncratic return and the market return. Although many studies have proved it in developed capital markets, it’s probably not applicable to the A-share market as there were strict restrictions on market-timing driven repurchases for a long time. In 2018, there was a huge shift in regulation policy which significantly relaxed restrictions on market-timing driven repurchases. Using a data set of 4939 monthly repurchases of A-share companies in 2013-2022, we examine the existence of market timing in A-share repurchases, the influence of the new repurchase policy and its mechanism. We use relative repurchase price (RRP) to measure the whole market timing effect and excessive return in post-repurchase portfolios monthly return (PPR) to measure the idiosyncratic component. Before the new policy, we find there is market timing but no idiosyncratic component. The new policy effectively improves the market timing effect and helps companies gain significant excessive return. We further explore the mediating effect of financial constrains in new policy’s influence. The new repurchase policy helps to ease the financial constrains in share repurchases by providing multiple new funding channels, thus improves the timing effect. Further analysis shows that the impact of the new repurchase policy is heterogeneous —— companies under greater financing constraints enjoy more improvement. To sum up, we draw three core conclusions. Firstly, the original policy’s restriction is an important reason for different market timing behaviors in A-share market from that of overseas markets. Secondly, the new repurchase policy improves the effect of A-share companies’ market timing in repurchases. It plays a positive role in increasing companies and shareholders’ wealth and stabilizing the market. Thirdly, in current market conditions, providing more financing channels is an effective measure of the new repurchase policy to improve market timing in repurchases. Proper use of the measure during market downturns can be beneficial.