Abstract: In the report, aimed at the problem of low bearing capacity of dredged sea sand, the direct shear test was performed to analyze the rigidity and shear strength of coir fiber reinforced soil. The results indicated that the mechanical properties of the soil can be effectively improved by adding coir fiber into the dredged sea sand, and the reinforcement effect increases with the increase of vertical stress on the reinforced soil. When the length of coir fiber is less than 5 cm, the reinforcement effect of coir fiber on the dredged sea sand increases with the increase of coir fiber length. The reinforcement effect decreases when the length of coir fiber reaches 8 cm. The rigidity and maximum shear stress of coir fiber reinforced soil increase with the increase of the content of coir fiber. When the content of coir fiber is less than 0.3%, the internal friction angle of reinforced soil increases with the increase of the content of coir fiber. When the content of coir fiber is more than 0.3%, the internal friction angle is almost constant.