The dynamic development of a city leads to idle land and idle building in the process of changing the land’s function. However, under the intensive urban development, the lack of public space implies the mismatch of space and function. The land and space under low-efficiency use needs to be re-activated and applied to create new value. Researchers have defined such “residual space” under different names but with the same intention: compared with the “formally” developed urban space with a rational plan, these ignored “unformal” space usually inspires true needs and willingness to reconstruct. By case study of architecture research and practice, teaching program in school of architecture, and interview of the people in such space, Urban China seeks to present potential ways to reshaping the residual space.