This paper is about land reclamation with hydraulic fill. The hydraulic fill is treated with microorganism for enhancing its compressibility. It selects Aspergillus niger, Agrobacterium radiobacter and Bacillus licheniformis to do the experimental study. First, the changes of the consolidation characteristics of fill soil are examined after different microbial strains and culture mediums are added in the soil through consolidation test. Then some measures including determination of specific surface area of soil particles, chemical composition analysis and mineral composition analysis are applied to exploring the mechanism of modified hydraulic fill with microorganisms. The results show that: after the incorporation of microbial strains and culture medium mixed with the soil samples, the compression factors av1-2 of the soil samples show a decreasing trend and the largest drop is 29%; the compression moduli Es1-2 show an increasing trend and the biggest gain is 37%. The mineral composition of soil samples is essentially the same. The high valent cation content reduces significantly, which isn’t the main reason of the change of soil compression feature. The specific surface area of soil particles added with Agrobacterium radiobacter increases 49%. The specific surface area of soil particles added with Bacillus licheniformis increases 45%. The reason is that strains change the connection state of soil particles, and then lead to increasing of soil particles or the change of soil structure.