Based on VaR(Value at Risk)this paper puts forward the concept of RaR(Return Rate at Risk) and analyses the result of RaR under the two common distributions to draw a conclusion that the relation between RaR,expected return rate and risk is linear.Based on that,the paper advances a new investment decision-making method.The study discovers that method can substitute the traditional utility function.Finally,we test the method through a case of portfolio selection.