Based on the theory of heat transfer and the mechanics of beam-slab-rail interaction,a refined thermomechanical coupling model for the bridge- mounted CRTS Ⅲ type ballastless track seamless lines was established to simulate the temperature field, longitudinal forces, and displacement variations of the track structure components under sustained high temperature environment ranging from 2~10 days. The findings elucidate a direct correlation between the escalation of sustained high temperature periods and the continual increase in temperature within the track structure, with an accentuated phenomenon of heat accumulation at deeper vertical strata. Additionally, there is a progressive reduction in the magnitude of the maximum positive temperature gradient, while the maximum negative temperature gradient experiences a gradual increase. Moreover, the longitudinal forces exerted on the steel rails and the longitudinal displacements of the track structure exhibit a cumulative pattern with the extension of the high-temperature regimen. In contrast, the longitudinal stresses within the track slabs, self-compacting concrete layers and slab demonstrate a decremental trend in correlation with the duration days.