Within the framework of heterogeneity in beliefs，this paper analyses the impact of different beliefs on asset pricing and the trading volume and gives the survival condition of investors． We find that investors with a more accurate expectation of the real return of risky assets can drive other investors out of the market． But the selection process can be very slow． Therefore，when we consider investment and asset pricing in a short period，the interaction of all investors should be considered，rather than only investors with a more accurate expectation． In fact，the existence of heterogeneous beliefs is the necessary condition for the trading volume and the changes of wealth and beliefs of investors play an important role in asset pricing． If we ignore the impact of heterogeneous beliefs，the partial results will be obtained．