The behavior of red blood cell passing through a micro-channel can be divided into two phases, where one is the transition phase and the other is the steady-state phase. This paper focuses on the in-depth understanding of the transition phase from the viewpoint of the physical significance. By using the customized threshold for classifying two phases on the red blood cells from different subjects, we show that the deformation of the cells plays a critical role in the location of the transition point. The technique of locating the transition point is improved by analyzing the evolution of R² value, which is used for locating the linear portion of motion profile. The experimental results are presented for supporting the proposed methods.