The anchoring grouting material has good performance and can effectively improve the service life of the anchoring structure. In order to solve the problems of insufficient stability and mechanical properties of traditional cement-based anchoring grouting material in slope engineering, nano-Al2O3 and waterborne epoxy resin were used to modify cement-based anchoring grouting material to obtain composite modified cement slurry. Through orthogonal experiment, scanning electron microscope and X-ray diffraction test, the basic properties and modification mechanism of composite modified cement slurry under different water-cement ratios and mix ratios were studied. The results show that the fluidity, setting time and compressive strength of composite modified cement slurry are more affected by the content of waterborne epoxy resin than that of nano-Al2O3. But the funnel viscosity and water seperation rate are more affected by the content of nano-Al2O3 than that of waterborne epoxy resin. The composite modified cement slurry has the characteristics of high stability, low water separation rate and high compressive strength, which effectively solves the problems of insufficient stability and mechanical properties of traditional cement-based anchoring grouting material. And there exists the best performance mix ratio: water-cement ratio is 0.5, nano-Al2O3 content is 5% (mass fraction, the same below), waterborne epoxy resin content is 20%, and curing agent content is 2.0%.