To solve the problem of moisture realtime detection in high salinealkali soil and high organic soil, this paper used time domain transmission (TDT) method to detect soil moisture based on phase detection. The probe of sensor structure and measuring frequency were analyzed in detail. The experiments showed that when the probes were 2mm in diameter, 10mm in interval, 120mm in length and the frequency was 100MHz, the measured performance was good to meet the demands of actual measurement. The measurement error of TDT soil moisture sensor in sandy loam, clay loam, salinealkali soil and high organic soil were ±0.87%, ±0.95%, ±2.20% and ±1.94% respectively, and the dynamic response time of TDT soil moisture sensor was about 4ms. The comparative analysis between foreign equipment TRIME (TDR) and domestic equipment BD-Ⅲ type soil moisture sensor showed that TDT soil moisture sensor of 100MHz could meet the requirements for detecting high salinealkali soil and high organic soil moisture in realtime. In addition, this device has good dynamic performance and stability with less technical difficulty and low cost but for good research and application prospects.