Abstract: Through compression test,shear test and sensitivity test,the structure of hydraulic fill is studied,and the result shows that the hydraulic fill microstructure has great influence on its mechanical properties,so it is a kind of strong structured soil.The soil samples are analyzed quantitatively by micro-structure SEM pictures of shear test,and the relation of the void and structure unit body microstructure parameter with axial strain is studied.The micro-structural effect of hydraulic fill shearing failure is analyzed in brief.It is found that the shearing failure process of hydraulic fill can be divided into three stages:(a) compression of gas in void and migration of the moisture content;(b) spallation of the pellet,grain slippage and structure damage;and(c) formation of new structure.