In view of the shortcoming of traditional fuzzy comprehensive evaluation, which is a coarse quantification of qualitative indexes without regard to holistic information in the evaluating process，a method of qualitative index quantification with fuzzy mathematics was proposed．Grey system theory was introduced into the multi-attribute fuzzy optimal selection of the design scheme, and the fuzzy optimal selection model was formed on the basis of the grey relational analysis．Taking a highway of Shanghai as an example, it proves that this model is feasible and effective when it is applied to the selection of the best treatment of the preventive maintenance of highway asphalt pavement．