Abstract: Since 1979, the urban park green space layout in China has undergone dramatic spatial differentiation and reconstruction. The complexity of the spatial structures and forms has restricted the exploration of the spatio-temporal laws. This research introduces the fractal theory that describes the structures and forms of the irregular complex system. Using three quantitative models of grid dimension, aggregation dimension and form dimension, and selecting six time nodes from 1979 to 2017, it probes into the fractal characteristics and rules of the spatial reconstruction of park green space in the main urban area of Nanjing City. The research finds that the reconstruction of park green space has gone through the regular quick filling stage, transformation stage of improving quality and efficiency, transition stage of stable quality and quantity, stage of in-depth optimization and adjustment, and stage of rapid increase of quantity and effect. The spatial composition is characterized by the maturing filling degree and equilibrium, and gradually weakening and disappearing self-affine and anisotropy. Meanwhile, the discrete situation of the funnel has transformed into a central agglomeration and gradually strengthened since 2012. The characteristics of the transition from homogeneous structure, heterogeneous self-structure to heterogeneous structure are outstanding. The integration characteristics of mountains, rivers, city and forests are becoming more prominent. With a view to enriching the park green space evolution theory, this research provides a planning basis and reference for the layout optimization, efficient allocation, and beautiful living environment supply.