Under the background of the reduction of industrial land in high-density cities, the “198” plot outside the urban development boundary of Shanghai, as a degenerate challenging urban site, plays an increasingly important role in the construction of urban ecological corridors. Under the new requirements of the new round of ecological corridor planning and the construction of five new towns, this study takes the “198” plot outside the urban development boundary as the clue and analyzes the spatial characteristics of challenging urban sites based on three scales of Shanghai, five new towns and typical new towns. The results show that “198” plot challenging urban sites are mainly concentrated in the ecological corridor, especially in the suburb green ring and the municipal ecological separation zone; The patch morphology is in a relatively unstable, very scattered, and uncompacted state, among which Pudong New Area is the most dispersed; The “198” plot challenging urban sites of the five new towns still have a large reduced land area, of which the “198” plot of Jiading new town and Songjiang new town are basically concentrated in the ecological corridor; The non-pollution type of “198” plot challenging urban sites in Qingpu new town accounts for the highest proportion (31.37%).