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Based on time domain transmissometry (TDT), measurement device for shrub stem water content was designed. This device consists of high frequency signal source, coaxial transmission lines, winding probe and phase comparison circuit. Propagation velocity of high frequency electromagnetic wave varies in different medium, and the propagation phase also changes. The dielectric constant of wet shrubs mainly depends on its moisture content. By measuring phase difference between the coaxial cable A and the winding stem probe B, the moisture content in shrubs was obtained. Absorbent cotton stick was choice to simulate shrubs with different moisture content. And the influence of the phase difference from frequency of high frequency signal source and the structure of the probe was studied. Experimental results show that under the conditions of 60cm probe length, 50MHz and 100MHz signal source frequency, the phase difference between the coaxial cable A and the winding stem probe B is monotonic with the change of water content, and there exists a good correlation between phase difference and moisture content.