【Objective】To delve into the temperature effect of sustained summertime heat on the bridge-mounted CRTS III type ballastless track, this research aims to offer scholarly guidance for the enhancement of seamless track line design, operational maintenance, and remedial strategies for bridge-mounted ballastless track systems.【Method】Based on the principles of thermodynamics and the mechanics of beam-slab-rail interaction, a refined thermo-mechanical coupling model for the bridge-mounted CRTS III type ballastless track seamless lines has been established to simulate the temperature field, longitudinal forces, and displacement variations of the track structure components under sustained high-temperature conditions ranging from 2 to 10 days.【Results】