Wheat powdery mildew is one of main disease damaging wheat production in China. As a main wheat production area North China and Huanghuai Region has a aggravating trend of wheat powdery mildew. Timely and accrate monitoring and prewarning of the powdery mildew has an important meaning to effective prevention of the powdery mildew and safety production of wheat. Based on wheat powdery mildew happening situation and chimatic feature of Beijing, Tianjin Municipalities and Hebei,Shandong,Shanxi and Henan Provinces,this paper quantizes response level of wheat powdery mildew to climate change, uses Bayes criterion to determine objectively happening grade threshold,considers the meteorological condition of wheat in growth period and key period,and finally presents corresponding assessment model. Research results show that the degree of accuracy being eomplete consistancy is 50%-90%,the degree of accuracy being basic consistancy is 85.7%-100%. The model may pre-warn and gride wheat powdery mildew prevention and control.