To investigate the deformation characteristics of salt rock subgrade filler under the influence of temperature, ensure the stability of salt rock subgrade, and promote the resource application of salt rock in subgrade engineering. The characteristics of phase transformation in brine and salt rock were analyzed comprehensively. An orthogonal test method was used to investigate the deformation of salt rock filler under the interaction of multiple factors in a single cooling condition. The salt expansion accumulation law of salt rock filler after multiple freeze-thaw cycles was systematically studied. Based on the test section field monitoring, the deformation characteristics of salt rock subgrade in salt lake area were evaluated. The results show the cooling curves of the different brine concentrations did not show any obvious subcooling stage, and the balance and fluctuation of the cooling curve are very short, and the brine phase transition temperature increased with increasing concentration. The cooling curve of salt rock filler has an obvious stage of subcooling and temperature jump, and the phase transition temperature decreases with the increase of the mixed brine concentration. The deformation of salt rock filler under single cooling condition ranges from -0.09 mm to 0.18 mm. The order of influence of various factors on the deformation of salt rock filler is overburden load > brine content > maximum particle size > compaction. The lower the concentration of mixed brine under the freeze-thaw cycle, the greater the salt expansion of salt rock filler. The overburden load has a strong effect on inhibiting salt swelling of salt rock fillers. Field monitoring of the entity engineering shows that with the growth of monitoring time, the deformation of the salt rock subgrade shows a sinusoidal cyclical variation, and the deformation decreases along the depth direction, the deformation of salt rock subgrade has a strong linear correlation with temperature.