Abstract: The displacement-time curve deformation of slope includes three stages: initial deformation stage, constant deformation stage and accelerative deformation stage.。According to former researches on different slope of the curve, definition of displacement tangential angle has already be put forward, based on what corresponding landslide pre-warning criteria has been set up also. However, due to different coordinate dimension of the horizontal and lateral axis, it is very difficult to make sure the accuracy of tangential angle. Based on displacement-time curve, by means of coordinate transformation, this paper has introduced a brand-new method to obtain tangential angles. By utilizing the improved tangential angle, the subdivided quantitative criteria for different stages and early pre-warning criteria for landslide are put forward. Furthermore, practical result has been achieved in terms of landslide monitoring and pre-warning by this method.