On the basis of field investigation and long-term monitoring results, the main factors that affect the mechanical performance of the Meridian Gate platform structure are studied by combining numerical simulation and experimental design method. This paper presents the results of the study in performance variation mechanism of the Meridian Gate platform structure through different aspects, i.e. freeze-thaw, partial water-saturation, differential vertical displacement at the bottom of platform, vertical load at the top of platform and coupled effect between the factors.The results show that the vertical load at the top, the uneven vertical deformation at the bottom and the partial water-saturation are main influential factors for the structural stress, and the number of freeze-thaw cycles, the coupled effect between the number of freeze-thaw cycles and the duration of partial water-saturation are also key factors for the maximum tensile stress in the area of arched doors; In the aspect of structural deformation of the Meridian Gate platform structure, the partial water-saturation, the differential vertical displacement at the bottom of platform and the vertical load are the significant factors. This study reveals the major factors and the influencing law of the mechanical performance of the platform structure and provides a scientific basis for the routine protection and preventative protection of similar heritage masonry structures.