In recent years, the use of Global Navigation Satellite System (GNSS) reflection signals to invert soil moisture has become a research hotspot, the use of spaceborne reflectometer data to invert soil moisture was a potential emerging technology. The paper took the data received by TechDemoSat-1 (TDS-1) satellite as an example, firstly, the theoretical relationship between Pr (the reflected signal power) and Mv (the soil moisture) was derived, and then the Mv obtained by the Soil Moisture Active Passive (SMAP)satellite was used as the standard value, in space, two trajectories of Pr and Mv were selected for Pearson correlation processing, the correlation coefficients on the two trajectories were 0.55 and 0.60, respectively. Then we carried out corresponding smoothing pretreatment for Pr and Mv respectively to remove the noise, the correlation coefficients obtained were all increased to 0.71, that was, Pr was strongly correlated with soil moisture. In addition, we took the data of four seasons: spring, summer, autumn and winter, and calculated the correlation coefficient between Pr and Mv was 0.78, which also showed strong correlation. The results show that Pr obtained by on-board GNSS-Reflections (GNSS-R) receiver and Mv have strong correlation and have the potential to estimate soil moisture.