The freezing characteristic curve describes the variation of unfrozen water content with temperature in soil and it is of engineering value to provide a calculation model for freezing characteristic curves suitable for different soil types. The freezing characteristic curves of six kinds of soil were tested by nuclear magnetic resonance technology and a method for determining parameters of Michalowski model describing the freezing characteristic curves of soil was given. The influence of initial water content and soil properties on freezing characteristic curve was analyzed and the model was improved by using the characteristics of Michalowski model parameters. The study shows that the freezing characteristic curve is independent of the initial water content, and the freezing characteristic curve of soil with different initial water content is the same during the freezing process. When the influence of soil supercooling is ignored, the freezing temperature Tf of soil is equal to the freezing point temperature of frozen water in soil and the freezing temperature of soil is not affected by the initial water content. Without considering the influence of temperature, the model parameter wa is approximately equal to the maximum of bound water content in the soil, which can be used as an important index parameter to analyze and evaluate the characteristics of clay. The practical value is improved by the single-parameter Michalowski model for it performs well in predicting unfrozen water content with less model complexity.