The application of the geosynthetic in expansive rock canal slope treatment of the South-to-North Water Diversion Project is illustrated. The operation methods of the geogrid, soilbag, geomembrance, etc., in the canal treatments are introduced. The field tests are carried out to preliminarily discuss the effect of different reinforcements. The research results show that two treament measures for the canal slope of expansive rock have certain protective effect, of which the geomenbrance with reinforcement possesses much better effect to antiseepage and restricting expansion deformation.