To provide a method for measuring soil moisture content in mass based on frequency domain reflectometry, a tube-pin type soil mass moisture content probe, consisting of a tube and a pin, was designed. Lou soil was used as sample to test the probe’s performance in measuring bulk density. At 50, 100, 150, 300 and 500MHz of the signal frequency, the influence of mass moisture content from 2.58% to 21.43%, bulk density from 0.80g/cm3 to 1.30g/cm3 and temperature from 10℃ to 50℃ on voltage ratio at probe to source signal were studied. Mathematical models describing the voltage ratio as functions of moisture content, temperature and bulk density were established. The feasibility of the models in predicting moisture content from voltage ratio, moisture content and temperature were analyzed. The results indicated that the absolute error of probe in measuring soil’s bulk density was within -0.129~0.016g/cm3. Soil moisture content, temperature, bulk density and signals’ frequency had obvious effects on voltage ratio. At 50, 100 and 150MHz, moisture content had obvious influence on voltage ratio. The model at 150MHz was better than the others at 0.01 significance level with the coefficient of determination of 0.8496. The absolute error between calculated voltage ratio and actual voltage ratio was within -0.166~0.159. The absolute error between calculated soil moisture content and actual moisture content was within -3.440%~4.039%.