Based on the unified traveling wave theory and transmission line model for reflective terminal with energy storage element， a formula for describing transient process from the initial traveling wave to steady traveling wave is deduced. It leads to a conclusion that the reflection factor is a time dependent function. The time-varying expression of the reflection factor at the reflective terminal with energy storage element and its span at different stages are presented. It is conventionally believed that the absolute value of reflection factor is always smaller than 1， but in fact， it is greater than 1 if there is an energy storage element at the terminal. In view of the fault component， the power polarity of the initial traveling wave is analyzed with both physical and mathematical method， with the conclusion that the terminal system is bound to absorb energy whatever its structure when fault is in the forward direction and that the absolute value of the reflection factor at the stage of the initial traveling wave is less than 1. The concept of the initial traveling wave stage is defined and its duration is given. A lot of digital simulation results have proved the validity of the theoretical analysis.