Multiple freeze-thaw cycle experiments were performed to determine the in-situ deformation of salt-frost heave of sulfate saline silt under long-term freeze-thaw conditions. For the determination of in-situ salt-frost heave of saline silt by removing the effect of water-salt migration due to temperature gradients, the in-situ salt-frost heave apparatus was designed to achieve a uniform cooling effect. The influence laws of four main factors, such as salt content, water content, initial dry density, and load, on the residual pore ratio of sulfate saline silt under the effects of freeze-thaw cycles have been analyzed. It has been found that sulfate saline silt with different initial pore ratios will eventually reach the same and stable residual pore ratio after multiple freeze-thaw cycles, independent of the initial compactness of the soil. At the water content was 16%, the residual pore ratio increased, then decreased and then increased again as the salt content increased. At the salt content was 3%, the residual pore ratio decreased linearly with the increase of water content. As the load became greater, the residual porosity ratio decreased. The accumulation effect of salt-freezing heave of residual saline silt could be effectively reduced at a water content of 16%, a salt content of 3%, and a load greater than 12.5 kPa. During multiple freeze-thaw cycles, the relationship between salt-frost heave deformation and pore ratio conforms to a linear negative correlation, and there was a positive correlation between the magnitude of accumulative salt-frost heave deformation and the magnitude of single salt-frost heave deformation. The equation of residual pore ratio with salt content, water content and load as parameters has been given in this paper. Using this equation, the prediction of accumulative deformation of salt-frost heave under long-term freeze-thaw conditions in residual sulfate saline silt in the seasonal permafrost region can be realized.