In order to explore the variation law of the permittivity (ε) of soil freezing process with different factors, taking the loess in the suburbs of Harbin as the research object, by changing the water content, dry density, salt and other factors, the ε changes in the soil freezing process were measured by the frequency domain reflection principle (FDR). And the influence of each factor on ε was analyzed. The results show that the effect of temperature on soil ε is mainly in the stage of soil water phase change. The change of ε with temperature in the room temperature is very small, and the error caused by FDR sensor measurement of water content in liquid water volume is not significant. Water content or dry density increases, the soil ε will be a corresponding increase; The increase in salt content will cause a sharp increase in ε, at this time directly measured by the sensor moisture content will be a greater error, the need for additional correction.