Freeze-thaw is a major source of damages for infrastructures located in cold regions. Investigating the effects of freeze-thaw on soil mechanical and thermal properties is important for the design and maintenance of infrastructures such as pavements and pipelines. Most existing research investigates soil behaviors in complete freeze or complete thaw conditions. Tools to assist the determination of freeze-thaw status are currently lacking. In this paper, we introduced the design of an innovative guided electromagnetic wave sensor called Time Domain Reflectometry (TDR) that can non-destructively monitoring the freeze-thaw process in standard specimens of soil and concrete. An analysis algorithm is developed to interpret TDR signals. Compared with the existing technologies, the new method not only accurately determines the various stages in the freezing and thawing processes, but also the degree of freeze-thaw status. This analyses algorithm is also independent of soil types and thus can be widely applied. Experiments were conducted on typical types of soils to validate the sensor performance. With the aid of this new sensor, the effects of the degree of freeze-thaw on soil mechanical properties (such as the modulus, strength and volume change) are determined. The success of our preliminary study indicates the innovative sensor and analyses we developed can be a useful tool for investigating the fundamentals of freeze-thaw effects on geomaterials.