Although the GM(1,1) model has been successfully adopted in various fields and has been demonstrated promising prospect. The paper adopts different form of grey model which is a supplement of the grey model and we call it GIM(1) model. On the analyzing the unequal GM(1,1) model the paper uses the difference quotient method to establish the unequal interval GIM(1) model. The examples prove the method in the paper is effective which improves the accuracy of the grey model. It provides an effective way for the grey system application.