By comparing the pros and cons of common methods of design evaluation, combined with the characteristics of oil tank design, the conversion of subjective factors to quantitative index is realized by using Fuzzy theory ,which is a method of mathematical analysis. On the basis of oil tank design index having been defined, an evaluation model is established to overcome the subjectivity of judges and achieve the scientific evaluation for oil tank design. The result shows that this fuzzy evaluation method is scientific, effective and reasonable.