Abstract: The slab track damage caused by thermal action will affect the high-speed railway operation safety, therefore, the exact solution about its temperature field is crucial. Based on the concrete random aggregate distribution algorithm and the heat transfer theory, develops a two-dimensional thermal transfer finite element model of the CRTSⅡ track at mesoscale to investigate the mesoscale temperature field. After the model’s reliability is confirmed by comparing the field measurements, the model is analyzed to determine the time-varying rule and spatial distribution rule of the internal temperature characteristics to the track at the mesoscale, and the two influence factors are the coarse aggregate maximum diameter and uneven distribution. The results show that the temperature field changes nonlinearly with depth at different time. The isotherm is generally parallel to the ground at the center of the track but fluctuates locally. The heat flux is preferentially transferred through the coarse aggregate passage, and its direction in the mortar points to the aggregates. The influence of the coarse aggregate maximum diameter and uneven distribution on the precast slab centerline temperature is almost negligible at different depths.