Based on the fuzziness and uncertainty of the subgrade stability in seasonal frozen area, the relative distance measure model with evaluation indexes and weights in the form of interval numbers is presented for the fuzzy synthetic evaluation of the subgrade stability. Firstly, the relative distance measure of each single index between the evaluated subgrade stability and the grading standards is defined. Then, the fuzzy synthetic evaluation model, which considers the functionality and proportionality of evaluation indexes, is established to calculate the comprehensive relative distance measure by using the Monte Carlo simulation method and the sequential relation analysis. Finally, a new decision index of the comprehensive relative distance measure is defined considering the concept of structural reliability, and the stability grade of seasonal frost soil subgrade can be determined by the minimum decision index from the corresponding grading standards. A practical example is given to demonstrate the feasibility and practicability of the proposed model.