Abstract: Firstly, through the hydraulic fill slurry settling column tests, the soil samples of the untreated hydraulic fill by the vacuum preloading were obtained, and the treated soil samples were achieved in the Tianjin Binhai New Area Lingang Industrial Area after being treated by vacuum preloading method.Secondly, all soil samples were transformed into micro-test soil samples and scanned by electron microscope to obtain SEM photographs.Finally, the micro-structure was quantitatively analyzed through micro-structure processing software, and micro-structure variation of the hydraulic fill during the course of vacuum preloading was researched, the result shows that the equivalent diameter, area, perimeter, shape ratio and roundness of void and grain were remarkably reduced, the number of void and grain increased significantly.The reason is that the original structure was destroyed and a new structure is formed in the process of the vacuum preloading.