The temperature distribution in steel-concrete composite girders is complex, existing specifications and studies for temperature gradients in such girders are inadequate as they fail to fully account for the influence of track slabs and ballast. Therefore, this study takes into consideration the effects of laying track slabs and ballast and conducts temperature field experiments on steel-concrete composite girders. A finite element thermal analysis model was established and validated by the experimental data, and the effects of track slabs, ballast thickness, and wind velocities on the temperature field is analyzed. Results show that ballast and track slabs with a thickness of 40 mm exert similar effects on temperature field of girder. Compared to an uncovered composite girder, they change the temperature distribution of the concrete slab from a reverse "C" curve to a top-to-bottom decreasing trend under cooling and from a top-to-bottom decreasing trend to uniform distribution during heating, increasing vertical temperature difference in concrete slab by 4 °C when cooling 15 °C. Interestingly, the steel-concrete interface exhibits temperature differences during all test conditions. The temperature gradient curve observed in the steel-concrete composite girders with railway pavement layers in this study reveals substantial deviations from the temperature gradient curve stipulated by existing bridge design codes. Parameter analysis reveals that, as wind velocities increase, the maximum vertical temperature difference decreases, and the thickness variation of the railway pavement layer within the range of 30–50 mm was found to have no discernible effect on the temperature gradient of composite girder. This study provides reference for research on temperature gradients in railway steel-concrete composite girders.