GM(1,1)model is the core prediction model in grey system.The study on the modeling conditions of grey system has been considered the base of improving the simulation accuracy.This paper adopts the method of combining theory proof and numerical example to study the modeling conditions of grey system,with the purpose to expand the class ratio judgment conditions of traditional grey prediction model.Results indicate that when the accumulate values of the raw sequence are equal,the development coefficient does not exist.The class ratio judgment intervals of the traditional modeling condition are not accurate enough,due to the still incomplete understanding of class ratio.Improving the smooth degree of the raw sequence is not the adequate condition to improve the simulation accuracy.Therefore,the modeling conditions of the traditional GM(1,1)model still need further research.