Abstract: In order to investigate deformation and failure of landslide under irrigation and evaluate the stability of the landslide, the authors took No.13 landslide at northern Jiaojiayatou of Heifangtai area in Gansu Province as a study case and performed field geological survey to analyze its characteristics of deformation and failure. On such a basis, the authors employed FLAC3D numerical simulation method to analyze the characteristics of deformation and failure under the constant water level, and then generalized the evolution law of landslide deformation. The results show that, under the condition of irrigation, early sliding of the landslide is mainly characterized by suffosion and sliding landslide, then the sliding landslide exhibits plastic flow and tension crack landslide and, with the further expansion of the slope and crack, the landslide shows a sliding mechanism of "pressing crack-shear failure".