In order to explore the influence of different ratios of compressive stress to roof and floor on the long-term performance of the bridge, this paper takes a long-span PC continuous rigid-frame bridge in Xiangxi Autonomous Prefecture as the research object, establishes the whole bridge model by Midas/Civil, and analyzes the changes of long-term stress and deflection of the main beam with different ratios of compressive stress to roof and floor by changing the longitudinal prestressed steel tendons. The results show that the greater the ratio of compressive stress between top and bottom plates, the better the long-term mechanical properties of the bridge.