首次公开发行（IPO）是公司筹集资金的重要途径，股票上市定价策略会影响公司募集资金金额。股票上市定价是一个重要的价格发现过程，可以反映市场参与者对公司的估值。香港是亚洲乃至全球的重要金融中心，其股票市场吸引了来自世界各地的投资者，使得香港股票市场在全球资本市场中占有重要的地位。香港股票市场也是连接中国内地和全球市场的重要桥梁，全球投资者可以通过投资港股来投资中国企业，并更好地理解中国市场。因此，研究香港股票上市溢价的影响因素具有一定的理论和实际意义。本文通过分析香港市场2011-2021年间的股票上市数据，发现股票上市溢价中位数是3.68%，但平均值达到61.8%，表明上市日的平均溢价受到极值的严重影响。本文以香港市场恒生综合股票指数的变动衡量市场情绪，通过多元线性回归分析，发现香港股票上市溢价率与公司上市前筹备发行阶段的市场情绪显著正相关。恒生股指在公司上市前30日内每变动+/-1%，新上市的股票上市日可能出现3.857%的价格波动。本文提出了两种可能导致股票公开发行价格被低估的解释，这两种解释与上市流程、信息错漏、风险补偿和利益分配有关。第一，发行人或保荐人可能没有充分意识到市场情绪对股票估值的影响，或者他们可能错误地估计了企业的真实价值。第二，发行人或保荐人可能为了对冲风险和保证稳健的收益，有意识地对股票公开发行估值进行了调整。这两种解释都考虑了市场情绪对上市溢价的影响。同时，本文以交易量为投资者关注中介变量，通过多元线性回归分析，研究了香港股票投资者关注程度与其上市溢价率呈现的显著负相关性，并提出三种解释。第一，上市日投资者关注可能反映股票估值争议。第二，上市日投资者关注的主要来源是承销商。第三，股票在上市日破发引起投资者关注，导致持仓者因回避损失而抛售。本文补充了香港市场股票公开发行相关文献的不足，特别是市场情绪、投资者关注程度方面的研究。本文首次验证了恒生指数变动率作为公开的、直接的市场情绪中介变量对上市股票价格短期变动的影响，解释了交易量作为投资者关注中介变量之一与上市股票价格短期变动的负相关性。此外，本文通过对上市日开市前竞价阶段的观察，填充了上市日开盘价形成机制方面的空白。

Initial Public Offering (IPO) serves as a crucial means for companies to raise capital, and the pricing strategy for offer price can significantly affect the amount of funds a company raises. IPO pricing is a pivotal price discovery process that entails market participants‘ valuation of a company. As a vital financial hub in Asia and globally, Hong Kong‘s stock market draws investors from around the world, positioning it significantly within the global capital market. It also serves as an essential bridge linking the Chinese mainland and global markets. Global investors can invest in Chinese companies and gain a better understanding of the Chinese market by investing in Hong Kong stocks. Therefore, understanding the factors influencing IPO underpricing in Hong Kong carries both theoretical and practical significance.Through the analysis of IPO data from the Hong Kong market between 2011 and 2021, this study finds that the median IPO underpricing ratio is 3.68%, though the average reaches 61.8%. This indicates that the average underpricing ratio on the listing day is significantly influenced by outliers. In this study, changes in the Hang Seng Composite Stock Index are used to measure market sentiment in the Hong Kong market. Through multivariate linear regression analysis, a statistically significant positive correlation is found between the IPO underpricing ratio of Hong Kong stocks and the market sentiment during the pre-listing preparation phase. For every +/-1% change in the Hang Seng Index within 30 days before a company‘s listing, the newly listed stock may see a price fluctuation of 3.857% on the listing day. This study proposes two explanations that might lead to an IPO underpricing, which are related to the listing process, information gaps, risk compensation, and benefit distribution. Firstly, the issuer or sponsor may not fully recognize the impact of market sentiment over stock valuation, or they may incorrectly estimate the true value of the firm. Secondly, the issuer or sponsor might intentionally adjust the valuation of the IPO to hedge risks and ensure robust returns. Both explanations take into account the influence of market sentiment on IPO underpricing. Meanwhile, trading volume is used as an intermediate variable for investor attention in this study. From multivariate linear regression analysis, a significant negative correlation between investor attention and the IPO underpricing ratio of Hong Kong stocks is investigated, with three explanations proposed. Firstly, investor attention on the listing day may reflect controversies in stock valuation. Secondly, the primary source of investor attention on the listing day could be the underwriters. Thirdly, a breach on the offer price on the listing day might draw investor attention, leading equity holders to sell off to avoid losses further.This study supplements the literature around IPOs in the Hong Kong capital market, particularly addressing gaps in research on market sentiment and investor attention. For the first time, it validates the Hang Seng Index‘s degree of change as a publicly available, direct measure of market sentiment, and its influence on short-term price fluctuations of newly listed stocks. This study also explains the inverse correlation between trading volume, acting as one measure of investor attention, and short-term price changes of newly listed stocks. Following observations of the pre-open auction phase on the listing day, this study fills a gap in the understanding of the price formation mechanism on the listing day.