Abstract: A multi period trade model including the rat, the institutional investor and the other individual investors was constructed. The rat trade not only changes the institutional investor’s utility, but also deepens the information asymmetry among investors. The model is resolved by using rational expectation equilibrium methods. Through the quantitative research, this paper shows that the market strike coefficient about rat trade decreases and the volume of rat trade increases with the trade time. But in the course of multi period rat trade, the other investors can not learn more information about asset value.