There are two distinctly different theories that could explain high IPO underpricing phenomenon in China stock market. One is pricing efficiency theory and the other is rent allocation theory. This paper selects IPO samples of A-share market from 2005 to 2012 to test two kinds of views above. Our findings indicate that the rent allocation theory was convincing only from 2005 to 2008. In comparison with the former view, the theory of pricing efficiency could better explain the changes of IPO underpricing since 2005 when the book-building allotment system was implemented.