Topographic change due to sedimentation and erosion of tidal flat is important for recognizing environmental changes and possible threatens. The tidal flat generally has small topographic variations and high moisture soil surfaces. The conventional SAR interferometric techniques cannot be used for generating DEMs in these tidal flats due to relatively short baseline. In this study, we developed a long-baseline airborne interferometric SAR (InSAR) system that has small ambiguity height and collected airborne InSAR data in the western coast of Korean peninsula. The constructed topographies using the long-baseline airborne InSAR were compared with GPS-RTK measurements.