The key issues in the theory of interval number fuzzy comprehensive evaluation are discussed in this paper, which includes weight interval calculation, quantitative index dimensionless method and etc. Due to the deficiency of “line method” for interval number formation, one improved method is given to increase the stability of interval number. Then the existing problems of several initial evaluation models are discussed, and the probability theory is introduced to improve evaluation model combined with coefficient of variable weight method. This improved interval number fuzzy evaluation method is adopted on one concrete cable-stayed bridge to general evaluate its safety and durability. The result shows that this improved fuzzy evaluation method can well reflect the general working status of the bridge and have good feasibility and practicality.