Abstract: When a tunnel engineering passes through a gypsum rock stratum, it often faces the problem of water suction and swelling of surrounding rock.As one of the expansion characteristics of gypsum rock, expansion potential has an important influence on the stress characteristics of tunnel lining structure.As one of the expansion characteristics of gypsum rock, expansion potential has an important influence on the stress characteristics of tunnel lining structure.In this paper, the gypsum rock of the Wuzhishan tunnel is taken as a sample.Based on the expansion characteristic test and BET specific surface area analysis, the criterion of expansion potential is determined.The influence of different expansion potentials on the stress of the lining structure of the Wuzhishan tunnel is analyzed by numerical simulation.The results show that the hydration degree of gypsum rock is negatively correlated with the expansion characteristic index and BET specific surface area.The expansion potential of gypsum rock can be quickly determined by the comprehensive expansion rate, expansion force and BET specific surface area.For the Wuzhishan tunnel, during the change of swelling potential of surrounding rock from non-expansion to strong expansion, stress concentration occurs at haunch and wall foot, tensile stress at vault increases, compressive stress decreases, and compressive stress at invert increases by about 12 times.The horizontal displacement of the whole primary support structure decreases, while the vertical displacement increases.The peak displacement increment is located at the inverted arch with the peak value of 2.14 cm, and the peak displacement growth rate is located at the vault with the peak value of 6.7 times.