The seasonal dry-moist variation of ECV soil moisture product developed by European Space Agency based on the microwave observations of multiple satellites is analyzed, and then the analysis results were compared with the station-based observations from National Meteorological Administration. Results show that the passive and active satellite data provide significantly different seasonal variation of soil moisture. In the summer monsoon region of East China, the passive data are characterized by a dry summer and a wet winter which are consistent with in situ observation. However, the active data has spatial difference of seasonal variation. The seasonal variation of soil moisture from active data is similar to the observations in North China, but it is in the opposite phase in the South China. The inconsistency of seasonal variations between them reveals that it is not a proper way to produce a multi-decadal soil moisture data in the summer monsoon region of East China by combining the passive and active microwave observations.