In this paper, process of slope failure is studied from phase of displacement (l) and its velocity (υ) along the slope. Velocity (υ) of displacement was calculated from the experimental data and the field data of slope failure, and the obtained date on υ and l are ploted on graph paper. It is found from these plots that process of slope failure expressed as tertiary creep contains two stages, which are called the first stage (I) and the second stage (II). In this failure process, the first stage (I) can be approximately expressed by υ=al+υ₀, and the second stage (II) is expressed by υ=υ₀ exp (b (l-l₀)).Solutions of these υ-l equations are expressed as: υ=υ₀ exp (at)(stage (I)), and υ=υ₀/ (1-bυ₀ (t-t₀))(stage (II)). It is confirmed from date analysis that equation for stage (I) and stage (II) are applicable to 1/υ-t plot of date on graph paper. The solution for stage (I) expressing 1/υ-t shows a linear relationship on semilog graph paper, and applied range of this solution holds with time most of process for tertiary creep.Final slope failure occures shortly, coming to range of stage (II), the plot of 1/υ and t at this stage becomes a linear relationship on normal graph paper.D