The transformation of social governance in the Megacity society is an important issue in modernizing national governance ability. The development process of Chinese Megacities not only reflects the general law of urbanization in other countries，but is also embeded in the context of Chinese l social transformation . Structural problems concerning national economy，population，social stratification，space and governance institutions in megacities are closely related to each other，which is the direct consequence of the original urban management system in China. All of these structural problems are playing essential role in improving social governance ability as actual questions which need to be solved as soon as possible. This paper summarizes the new features of the structural problems and their impact on the transformation of social governance system in megacities. Furthermore，the paper introduces successful developmenl experience of other international metropolises and analyses the connotation of the concept “governance”. In addition，several policy recommendations are proposed for the transformation of the social governance institutions in megacity at the end of the paper.