To ensure that the comprehensive bearing capacity of the existing structure in the reconstruction and expansion project meets the requirements, the main structure of the reserved Line 3 underground station as the background of the study, the use of on-site measurements and the combination of AHP-FUZZY mathematical modeling method to study the long-term service structure in the mechanical properties of the discount. The results show that: (1) the existing station structure exists some decorative layer falling, concrete spalling, water accumulation, water seepage and other problems detection, the station hall level and entrances are not seen the existence of structural damage; (2) the concrete strength of the reserved track interval of Line 3 is about 27.2 MPa ~ 43.7 MPa, the depth of carbonation of the side walls is 17 ~ 27 mm, and carbonation of the base plate did not occur; the thickness of the protective layer of steel reinforcement is about 50 ~ 80 mm, the probability of no corrosion of steel reinforcement is more than 90%; (3) the structure of the pre-built station has different degrees of deterioration, and the bearing capacity and durability effect has deteriorated, which will affect the safety and stability of Line 3 and the reconstruction and expansion of Line 3，The results of the study can provide a reference for the durability and life prediction of the long operating metro stations.