Abstract: The method of using the dielectric constant of the soil to determine the soil volumetric water content has been used widely by researchers. There exist a lot of works on TDR which can also measure the soil volumetric water content, but little research about the 5TM water content sensors. On one side, there almost has no research on 5TM in various soil; on the other side, the applicability evaluation of 5TM in sub-zero is unknown. In this study, three kinds of test materials were used, a Qinghai-Tibet red clay, a silt and a Micro silica. First, we analyzed the relationship between the dielectric constant and the soil volumetric water content, we revised the Topp(1980)formula and determined the value of a and b in Ledieu formula. Besides, a logarithmic formula to confirm the soil volumetric water content was proposed. By comparison, the fixed Topp formula can be used in all kind of test materials, this empirical formula gives a good response to the relationship between the dielectric constant and the soil volumetric water content. Second, by comparison the results with NMR, a new - empirical equation of saturated Qinghai-Tibetan red clay in freezing condition has been proposed, and the applicability evaluation of 5TM in heat and moisture of frozen soil has been researched.