In this paper, the mathematical model of Fuzzy comprehensive judgement of the division of the north sub-tropical belt is preposed.The division of the north sub-tropical belt in Shaanxi province is carried out with this model, the concrete location is defined, and the quantitative problems of transitional belt and indices are solved.This not only changes the traditional qualitative division of the north sub-tropical belt into quantitative one and promotes its accuracy, but also liberates the division of boundaries from absolute affirmation and negation, and thus various transitional states appear.