Sand widely distributed in engineering is easy to cause a series of engineering geological disasters due to its loose structure and poor engineering properties. In this paper, the unconfined uniaxial compressive characteristics of sand reinforced by polyurethane polymer and sisal fiber were evaluated, and the micromechanical mechanism of sand reinforced by different curing agent and fiber contents was analyzed by electron microscope (SEM). With the increase of curing agent content and fiber content, the elastic modulus, compressive strength and toughness of sand soil increases significantly, and the failure morphology of the sample changes from "petal-like" to suture line shape with the increase of fiber content. Polyurethane enhances the reinforcing effect of fiber by improving soil-soil/fiber interlock force, soil-fiber bonding force and soil-fiber friction force.