Taking urban agglomeration as the main object to optimize the spatial layout of urbanization is an important part of constructing the national land spatial planning system, and the essence of spatial optimization is to promote the coordinated development of large, medium and small cities within the urban agglomeration. Based on the measurement of urbanization coordination level of 26 cities in the Yangtze River Delta Urban Agglomeration from 2001 to 2016, this paper analyses and identifies the urban coordination relationship by using the methods of social network and multi- dimensional- scaling, and explores its internal evolution mechanism. The results show that: (1) With the improvement of the urbanization coordination level of the cities in the Yangtze River Delta Urban Agglomeration, the internal space of the urban agglomeration is obviously changed. The high coordination cities gradually show a Zshaped distribution with Shanghai as the core, and the low coordination cities were stably distributed in the expanded area of the urban agglomeration. (2) According to the correlation strength of the coordination level of the Yangtze River Delta Urban Agglomeration, the cohesive subgroups were divided. The values of weighted average centrality and the contact density of the cohesive subgroups of the urbanization coordination relationship increased, and the polarization effect of Shanghai was more obvious. (3) The coordination structure of the urban agglomeration was identified from two dimensions of space and time. The Yangtze River Delta Urban Agglomeration has transformed from the "circle layer" structure centered on the provincial capital cities under the influence of spatial distance into the structure of "coreperiphery" under the influence of temporal distance. (4) The evolution of spatial structure of the urban agglomeration was influenced by the change of coordination level of population, land and economy urbanization. Compared with population and economy urbanization, land urbanization has a significant role in promoting the level of urban coordination. The optimizing policies of the Yangtze River Delta Urban Agglomeration were proposed from the perspective of coordination after analyses of its spatial structure. This is conducive to the realization of the integration of urban agglomeration and the efficient use of space resources under the conditions of China's existing resource and environmental carrying capacity. [ABSTRACT FROM AUTHOR]