Abstract：Through the analysis on deformation property and the basic constitution of different stability evolution stages of the accumulative-formation slope，it is found that the surface displacement vector angles of slope are constituted of whole sliding vector angle，compressive displacement vector angle，plastic deformation vector angle and creeping deformation vector angle. And the ratio of its constitution is varied with different position and the different stability evolution stage. The formation mechanism of displacement vector angles in different stability evolution stages of the accumulative-formation slope is deeply analyzed and explored. The quantitative relationships among surface displacement vector angles，displacement velocity，the other parameters in the stages of the compressive deformation and the plastic deformation are established，respectively. The variation laws of displacement vector angles in the different evolution stages and different positions are also summarized. Finally，based on the analysis on the actual displacement monitoring data of the different evolution stages of Xitan landslides，it is found that the displacement vector angles of the slope are of different variation laws in different stability evolution stages，and these dynamic variation laws are coincided well with the actual landslides stage.
