Analysis of Ashare market of Shanghai Stock Exchange shows that, in bullish market, the returns of stock portfolio capital with trading codes ended with “4” are lower than necessary returns of the market under allowed risk level and that the display of other portfolios is not obvious, which indicates that China’s investors have bias on stock trading codes and deliberately avoid the stock trading codes ended with “4” , and, furthermore, the return on the portfolio constituted by stocks with trading codes ended with “4” is significantly impacted, however, the bias on the propitious numbers such as “8” and “6” is not marked, meanwhile, the behaviors that the investors shun “4” are clearly displayed when stock market is bullish but trend to disappear when stock market is bearish, which demonstrates that the investment behaviors of the investors are rational under bearish market. 