Abstract: In the light of the classification standards of crude oil with four factors, a new method of fuzzy classification analysis for crude oil is developed. The key of this method lies in the determination of membership grades and weights, while their determinations are usually influenced by various personal factors largely. This must affect the reasonableness of the evaluation results severely. Therefore, according to the assessing subjects and factors and objects, this paper presents a new idea for their weight to be determined by the grey relational grades based on the referential factor, viscosity of crude oil. At the same time the formula ot the membership grade for each factor is deduced according to the properties of mountain-type curve series. The basic principle, processing method and practical application are discussed. This method is scientific in thoery and very ease programming, which provides an effective means for the classification of crude oil.