Abstract: By a series of laboratory tests, the effect of the grain size distribution of silt soil on the mechanical property of 2:8 lime-soils is studied. The silt soil from construction site is divided into three kinds of groups with different grain size composition, coarse, medium and fine grain size group, and combined with lime in different ratios to form 2:8 lime-soils with different grain size distribution. Soil mechanical tests show that the strength of lime-soils is become higher with the increase of soil grain size, and the highest strength comes in the lime-soil with combination of coarse and medium grain size soils which may reach 1162kPa. Comparison between micro-structures of clean soil and lime-soils observed with electron microscope reveals the reason of the enhancement in mechanical strength of lime-soil.