To evaluate the effectiveness of locust bean gum (LBG)and sisal fiber (SF) for improving red clay, laboratory unconfined compressive strength tests and numerical simulation methods were employed. The unconfined compressive strength response characteristics and the microscopic structural damage mechanisms of the improved red clay were investigated. The results show that LBG and SF significantly promote the compressive strength of red clay. The compressive strength of the unimproved red clay is 75.5 kPa, and that of the improved red clay reaches 888.3 kPa when the mass fraction of LBG and SF is 4% and 0.6%, respectively. The microcracks of the red clay improved by the composite material are mainly diamond-shaped, and their number decreases with the increase in the mass fraction of LBG and SF, with shear microcracks dominated. LBG and SF can effectively improve the strength of the contact force chain between soil particles and enhance its resistance to damage and deformation. With the increase in the mass fraction of SF, the non-orientation of the contact force chain is stronger, and the transmission direction is richer. There is a synergistic effect between LBG and SF in improving the microcosmic mechanism of red clay, and the improvement effect of their composite material is better than that of a single material.