中文摘要：

从理论和实证两方面，研究上市公司股权再融资（SEO）时是否更换承销商的决策问题以及承销商变更对上市公司资本市场表现的影响．理论模型表明，当承销商和发行公司之间存在较为严重的信息不对称，即在首次公开发行（IPO）时，不同资产质量的公司都能获得高声誉承销商承销；而当发行公司和承销商对彼此状况了解更为深入，即SEO时，高声誉承销商能识别不同公司的资产质量，出于对自身声誉的维护，不再承销低资产质量的公司，此时低资产质量的公司只能选择低声誉的承销商．实证结果与理论模型相符合，实证发现：相对于质量好的公司，质量差的公司在SEO时被迫更换承销商的概率更高．更换组公司与未更换组公司在IPO时雇佣的承销商声誉没有显著差别，而更换组公司在SEO时雇佣的承销商声誉明显较差．进一步探究承销商变更对公司市场表现的影响时，发现相较于更换了IPO承销商的公司，未更换承销商的公司在SEO时能够获取更低的折扣率和更高的长期股票回报率，这一结果在多种测试下都是稳健的．

英文摘要：

This paper examines the decisions underwriters and issuing firms make during seasoned equity offer- ing and the impact of underwriter switch on the price performance of issuing firms. Our theoretical model shows that when there is a severe information asymmetry between the underwriters and issuing firms （IPO）, all firms can choose reputable underwriters. As firms and underwriters know each other further and deeply （SEO）, reputable underwriters can know the real asset of issuing firms and may refuse low-quality firms to maintain their reputation. Therefore, low-quality firms can only choose bad reputation underwriters at the SEO stage. The empirical results are consistent with the theoretical model： low-quality firms have to switch under- writers during the SEO period. There is no significant difference between a switcher and non-switcher during IPO, but underwriter reputation of a switcher is worse during the SEO. Meanwhile, firms managed by former IPO underwriters exhibit lower discount levels and better long-run performance compared to the firms that switch their underwriters, and this result is robust to various checks.