中文摘要：

本文以新股上市首日股价大涨这一现象为例，探索了股市交易中群体行为的发生机制。第一，股市群体行为的发生往往具有特定的外部市场、制度环境因素作为铺垫。第二，突发事件或者新生事物的出现会对群体行为的启动起到激发作用。第三，具有易受环境因素影响而聚集，易受激发因素影响而采取共同行动的大量个体投资者的存在，使群体易于聚集和形成。第四，部分账户大笔委托的“煽风点火”和“推波助澜”、高风险偏好投资者的积极参与，是群体行为得以持续并加强的必要条件。最后，证券交易过程中以“行情”为纽带的群体互动和情绪传染，最终导致了群体行为的形成。基于此，本文认为，应当推进交易制度创新，建立投资者分类教育机制，完善投资者适当性管理制度，同时强化对“炒新”行为的监管措施。

英文摘要：

In this paper, we analyze the cause of the herd behavior in the stock market trading by studying the big rise phenomena during the IPO first day. We found that there were always specific external market and institutional environment factors when herd behavior happened. Sudden events or new events could stimulate the herd behavior. The existence of individual investors who are easily influenced by the environment and stimulus will make the groups tend to form. Some accounts with large amount entrusted investment, active participants willing to take high risk, are both the requirement to sustain and strengthen the herd behaviour. Finally, the interaction and emotional spreading between investors during the stock trading cause the herd behaviour. We suggest promoting the trading system innovation, developing education system for classified investors, perfecting the investor appropriateness management system, and strengthening the supervision on the ＂chasing new＂ behaviour.