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In order to measure the soil moisture in real time, quickly and accurately by using time domain measurement technique, a low cost soil moisture measuring meter was designed based on time domain transmission (TDT) principle. The probe of TDT meter adopted structure of closed loop, so that the signal was transmitted on the probe in one way. The permittivity of soil was measured by measuring the transmission time of electromagnetic wave in soil medium, and the soil moisture was obtained through soil calibration equation. TDT meter was composed of a high frequency pulse signal source, a coaxial transmission line, a probe in U-shaped loop structure, a transmission time measuring circuit using TDC-GP2 time interval measurement chip as the key component and a control circuit using LPC2132 ARM micro controller unit as key component. Through the standard solution test and soil test, it was proved that the measurement results of TDT meter with double U-shaped probe were better than those of single U-shaped probe. The root mean square error (RMSE) of transmission time measurements by using TDT meter with double U-shaped probe was 43.9ps, and the RMSE of dielectric constant measurements was 0.791. Using TOPP equation, the RMSE of soil moisture measurements in sand soil determined by TDT meter was 0.029cm3/cm3, and the RMSE of soil moisture measurements in loam soil determined by TDT meter was 0.039cm3/cm3. The results showed that the soil permittivity and soil moisture could be measured accurately by using TDT soil moisture measuring meter.