Abstract: To reduce the erosion of the loess slope under the condition of rainstorms, the loess cured by guar gum is used to protect the slope surface. The engineering properties and erosion resistance of the guar gum-reinforced loess are studied by conducting the direct shear test, penetration test, slope scour test in simulated rainstorm, and the curing mechanism of guar gum is studied by contrasting the microstructure characteristics of plain loess and reinforced loess. The results show that the guar gum can effectively enhance the shear strength and the anti-permeability of loess. The cohesion and internal friction angle of the reinforced loess show the same trend, and they increase first and then decrease with the increasing guar gum content, and increase with the increasing curing age. The saturated permeability coefficient decreases with the increasing guar gum content and curing age. Compared with plain loess, the cohesion and internal friction angle of 7 d cured loess with 1.0% guar gum content increases by 53.7% and 5.6%, and the saturated permeability coefficient decreases by 78.3%. The slope protection effect of the guar gum-reinforced loess under rainstorm scour condition is obvious. Compared with the slope without protection, the cumulative scour amount of the slope decreases by 64.4%, and the average slope flow rate increases by 55.2%. The strengthening mechanism of guar gum on loess mainly lies in the high viscosity hydrogel produced by its hydration reaction to fill the pores and cement loess particles. This study provides test support for the application and promotion of the guar gum-reinforced loess in slope protection engineering.