The basic principle of time domain reflectometry used for soil moisture measurem ent is introduced, and the disadvantages of currently available TDR instruments are discussed as well as their advantages. A new TDR system, called P〖CD*2〗TDR , composed of a highfrequency signal generator, a phase detector, a microproce ssor and a soil moisture probe is developed. Singlefrequency sinusoidal voltag e signal is adopted as test signal, and the travel time of the test signal along with probe embedded in moist soil is measured by a phase detector instead of hi ghspeed sampling oscilloscope, from which the soil water content will be estim ated. It has high accuracy and resolution in travel time measurement. Calibratio n experiments are conducted in sand, loam soil and clayey loam soil samples with the volumetric water contents varied from zero to saturation. The experimental res ults show that the measuring deviation is less than 003 between P〖 CD*2〗TDR and gravimetric sampling method. 