Shallow cohesive soil interacts strongly with the atmospheric environment, and its engineering properties deteriorate severely due to the influence of climate factors, leading to geological disasters and ecological environmental problems. In response to the above issues, a combination of bio-glue and rice straw fiber was introduced to improve the mechanical properties of cohesive soil. Through unconfined compressive strength tests and direct shear tests, the changes in the unconfined compressive strength characteristics and shear strength parameters of soil with single admixture and composites were investigated. The effects of bio-glue and fiber contents on the improvement effect of composite treatment were studied, and the effect mechanism of bio-glue and straw fiber composite modified cohesive soil was analyzed based on scanning electron microscope (SEM). The results show that due to the increase in bio-glue content and fiber content, the stress-strain curves of modified soil tend to behave as strain hardening, with a prolonged peak position and reduced post-peak stress decay. Both unconfined compressive strength and shear strength of modified soil are significantly enhanced, which mainly enhances the soil’s mechanical properties by increasing cohesion and has little effect on the internal friction angle. Bio-glue improves soil structure through surface coating, particle bonding, and pore filling, which also improves the reinforcement effect of fiber-soil interface and enhances soil’s mechanical properties by combining the network framework formed by fibers.