Wetlands cover more than 4% of the Earth's land surface and include hydrologic and other process that are fundamental to understanding ecologic and climatic changes. It is very important for wetlands protection and re-construction to measure water level changes and consequently water-storage capacity changes in wetlands. Using VV polarization C-band and HH polarization L-band SAR data, combined with synchronous field measurement and investigation, this paper analyzes the difference of backscattering and interferometic coherence characteristics of different types of wetlands. After evaluating factors that influence interferometric coherence, the framework, for measuring water level changes using InSAR phase information, is presented in this paper. With obtained SAR data, this paper studies the InSAR-derived water level changes in Yellow-River Delta wetlands. The results show that the InSAR technology has a great potential in mapping water level changes in coastal wetlands, and InSAR-derived water level changes can supply unprecedented spatial details.