This paper selects IPO data from 2006 to 2011 in China A share market,and studies the relation between speculative behavior in new share and IPO underpricing using a multiple regression model. The empirical results indicate that speculative behavior in new share and IPO underpricing is significantly positive correlation. The indicators that reflect speculative behavior in new share have a significant positive effect on IPO underpricing. The indicators include initial market capital,turnover rate on the first day of IPO,and stock price fluctuation degree on the first day of IPO.