Abstract: The key of using the technology of time domain reflectometry (TDR) is to establish the empirical equation for the relationship among electromagnetic parameters, water content and dry density. Based on the one-step method, two empirical equations are established for the content, dry density, apparent dielectric constant and drop volt parameter, which can calculate the water content and dry density respectively. Then the influence laws of compaction energy, pore fluid conductivity and temperature on the calculated results by the new equations are analyzed. After calibration, the relative error of dry density is within ±5%, and the error of water content is within±0.02 g.g^-1. Meanwhile, an adaptive method is proposed to test the water content and dry density by using the TDR method conveniently and efficiently in the field tests in which the calibration tests may not be comducted.