The underpricing of initial public offering(IPO) has been one of the "the new issue puzzles" in the finance.The paper studes the underpricing of IPO phenomenon by real option methods.The research find that even the information of stock market is symmetry,the underpricing of IPO is inevitable.With the development of stock market,the(degree) of the underpricing of IPO will be lowed.The reasons of underpricing of the IPO in Chinese stock market,on the one hand come from widespread existing IPO underpricing,and on the other hand,come from the irrationality of IPO pricing way and stocks is not all circulate.