Soil freezing characteristic curve（SFCC） represents the relationship between the freezing temperature and unfrozen water content. The SFCCs of clay samples saturated by different concentrations of Na Cl solution are obtained using the nuclear magnetic resonance（NMR） and the cold bath. The effect of pore solution at different concentrations on the SFC is analyzed. It is shown that with the increase of the solution concentration

the freezing characteristic curve moves upwards

that is

at the same unfrozen water content

the freezing temperature decreases with the increase of the concentration. It is mainly because the osmosis potential induced by salt solution lowers the total potential of soil water

which in turn depresses the water freezing point. The freezing temperature is related to the energy status of liquid water in frozen soils. The total pore water potential includes the matric potential and the osmosis potential

where the matric potential includes capillary and adsorption and the osmosis potential depends on the concentrations of pore solution. When the unfrozen water content of the sample is very low

the adsorption effect is available. At this time

the unfrozen water is adsorbed on the soil particles in the form of adsorbed film. Similar to the unsaturated soils

a relationship between intermolecular forces and adsorbed water film is used to describe the soil freezing characteristic curve at low water potential. Combined with osmotic potential

the freezing characteristic curves at different concentrations are simulated

and the fitting results are in good agreement with the experimental data.