Taking Nanjing old south area as an example, this research analyses the changes and problems of the plot division mechanism since 1949 and its impact on urban forms. Changes in the plot division mechanism show that megaplots have been a constant in the ever-changing land development system since 1949, leading to elimination of historic land subdivisions. In this sense, it is necessary to establish a set of smart plot division strategies to promote the restoration of this historic urban area.