Research conclusions: (1)The stability of dyke in declining gully is influenced by the lowering base gradient，the cohesion of base contact surface and friction coefficient．(2)It is inappropriate to build a dyke on the ground directly when ditch gradient is more than 5％，and the dyke base should be made flat if possible．(3)It is appropriate to regard the cohesion of base contact surface as zero because the base contact surface is immersed in water for long term to drop the cohesive performance．