Abstract: In order to study the different physical and mechanical properties of unsaturated soil filled with air or CO2,this study focused on the hydraulic reclamation fine sand along the Changjiang River.We manipulated water content of the fine sand samples filled with air and CO2 respectively and carried out a consolidated undrained triaxial compression test on them.We analyzed the stress-strain curves and shear strength indexes of the fine sand under the action of air and CO2.The results indicated that the fine sand′s stress-strain curves exhibited a strain softening type under low confining pressure and a hardening type in high confining pressures.Fine sand filled with CO2 had low porosity and high compactness, resulting in greater shear strength compared to fine sand filled with air.In high confining pressures, the fine sand particles were more closely interconnected, and stress transfer was more relied on the particle skeleton, so the difference in shear strength of fine sand under the action of two gases was reduced.Increasing the water content of fine sand from 4% to 12%,the cohesion force of fine sand filled with CO2 were 2.62 to 4.37 times larger than that of fine sand filled with air.The effect of different gases on the internal friction angle of fine sand can not be ignored, which lies a theoretical basis for unsaturated fine sand consolidation by filling CO2 into it.