After the untradable shares reform the major shareholders of IPO companies that issue may sell their shares after market. This paper investigates a sample of 555 IPOs issued and listed in the Ashare market before and after the reform, and the empirical results indicate that the total proportion of the second to tenth biggest shareholders’ shares is significantly positively related to the IPO underpricing rate and negatively related to the abnormal return of the thirteenth month after the first day, while that phenomena does not exist before the reform. And these results suggest that the major shareholders may sell their shares in large immediately after the restricted period of 12 months, and in order to obtain higher profits when they sell shares later, they may be incentive to push up the firstday price, which leads to an extremely high IPO underpricing rate.