The forecasting of the failure time of a slope remains a worldwide problem because of many different possibilities of geological conditions in combination with many varying external factors such as climate and vegetation, and not well-defined or unknown time effects in deformation and failure models. The aim of this paper is to suggest a new method to carry out the phase division and to explore tangential angular features of the displacement-time curve of creep slopes as well as the acceleration characteristics in the process of slope deformation and the pre-warning criteria for critical failure. An imminent failure is pro-ceeded with usually three basic deformation phases, namely primary creep (“decelerated”), secondary creep (“steady-state”) and tertiary creep (“accelerated”). Mostly, only during the accelerated phase the imminence of a possible slope failure is rec-ognized. The analysis of displacement data from a series of landslides allowed to recognize different evolutionary patterns of displacement. A quantitative approach was proposed to describe the tangential angle of the displacement-time curve and a new criterion based on the angle was put forward to divide the accelerated phase into three sub-phases: initial acceleration, medium acceleration, and the critical failure. A pre-warning criterion for critical failure is also proposed consequently. Changes of acceleration showed completely different characteristics from those of cumulative displacement and displacement in the process of slope deformation. The values of acceleration usually oscillate around 0 prior to the critical failure phase, whereas the acceleration increases abruptly when the deformation moves into the critical failure phase. This allows, therefore, for a method to forecast the time of the failure. So it is possible to define different alert acceleration threshold values to be used for emergency management.