Abstract: In order to meet the requirements of fluidity, stability and safety of grouting materials for cracks in canal slopes in expansive soil areas, a composite grouting material was prepared by using local weak expansive soil as the stabilizer, combining with ultrafine cement and fly ash.The viscosity, water separation, stone strength and density characteristics of the composite slurry were studied.The influence of different water-solid ratio and material ratio on the performance of grouting materials were explored; and the micro structure of the stone body was analyzed by SEM scanning.The cementation of the slurry-soil interface after grouting was discussed by indoor simulation test.The results showed that the slurry with the water-solid ratio of 1.0 has good fluidity and stability when the mass ratio of expansive soil is between 30 % and 70 % and fly ash is between 12 % and 24 %.Reducing the water-solid ratio and increasing the content of expansive soil can reduce the drainage rate of composite slurry and improve the stability of slurry.Adding fly ash can improve slurry fluidity; after grouting, the slurry water penetrates into the soil, accompanied by the migration of cementing materials, forming a transition layer at the interface between the slurry and the soil, which is conducive to the bonding between the two.The research results can provide a scientific basis for the selection of crack grouting materials for expansive soil canal slope.