Residential area detection is extremely important for supervision of rush-built and illegal construction behavior to protect arable land and basic farmland.Traditional manual recognition of illegal construction is simple but time-consuming.The specific research work in the thesis includes: the proposition and designing of a multi-scale segmentation method based on watershed segmentation combined with region merging algorithm,comparative experiments of the new algorithm and traditional algorithm.Then,architecture extraction experiment based on the multi-scale segmentation method is carried out and analysis of the precision of comparative experiment results of pixel-based and object-oriented extraction methods is made,all these steps facilitate the automatic mapping of the architecture.