Abstract: The time-domain reflection method (TDR) based on the time-domain carrier-free pulse principle can test volumetric water content of soils timely and accurately and is widely applied in geotechnical engineering. But all the TDR testing instruments are imported at present, and some foreign countries implement blockade on the techniques. A set of TDR system based on the principle of stepped-frequency is recommended. The output frequency component of the signal source can be accurately known and the noise in the received signal can be effectively restrained. A reasonable probe converter is developed to avoid blind spots in normal testing area and to improve testing range and accuracy. Finally, the effectiveness of the new TDR testing equipment is verified by comparing the volumetric water contents of water, air and soil.