TDR (Time Domain Reflectory) is a type of equipment for measurement of soil water content. The travel velocity of electromagnetic wave is determined by the dielectric constant, and the dielectric constant of soil is determined by the soil water content. TDR can measure the soil water content by measure the travel velocity of electromagnetic wave. A set of TDR system and its measurement are introduced. Calibration for TDR measurement was done in the laboratory and the field. The result shows that the calibration has to be done and the field calibration is practicable, and the prediction equation can be used in other area of the Loess Plateau. Because TDR can measure soil water content automatically and continuously, this method is recommendable.