The main purpose of this paper is to evaluate electrical treeing degradation for cable insulation. To effectively deal with the currently facing issues, I endeavor to find the most optimal methods by means of applying signal process. First, we made three type models of electrical tree for PD generation to show the distribution characteristics and applied voltage to acquire data by using a PD detecting system. These acquired data presented distribution and four 2D distributions. Hn(q), Hn(), Hqn(), and Hqmax() were derived from the distribution of partial discharge. From the analysis of these distributions, each PD model is proved to hold its unique characteristics and the results were then applied as basic specific qualities for insulation conditions. In order to recognize the progresses of an electrical tree, we proposed methods using scale parameter by means of Weibull distribution. We measured the time of tree propagation for 16 specimens of each model from initiation stage, middle stage, and breakdown respectively, using these breakdown data, we estimated the shape parameter, scale parameter and MTTF(Mean Time To Failure). The results of this study recognize the sources of PD by applying acquired data from PD signals to pre-acquired data. If the cause of PD is degradation, in other words, electrical tree, we can determine the replacement time of devices at the initiation stage of tree growth progress or no later than the middle stage and use it as a basic methods analysis diagnosis system. That is, pattern recognition and Weibull distribution can be employed to get the reliability of diagnosis.