This paper uses normalized elements in the sample database to avoid the influence of index type and dimension. Basing on the index system and grade standard of tunnel health safety assessment, it puts forward the relative difference function of variable fuzzy set by the method of set pair analysis and confirming reasonable the relative membership function of the related health indexes in every level and its level standard interval, and develops the assessment model of tunnel health after confirming the relative indexes right by multiplication scale method. Once confirming the eigenvalue of health levels, some samples are given to verify the scientificity and rationality of the method in, the results show that the calculation process is visual, simple, strong currency, result is reasonable and precision is high. The model can be used for various system assessment problems and it’s propitious to promote the more use of variable fuzzy sets in the field of civil engineering.