A partial discharge（PD） signal measurement system is presented and the statistical characteristic of PD with aging time for twist pair is investigated under continuous square pulse voltage. According to comparison of responses of sensors made of different core material， the sensor made of the NiZn ferrite is more suitable for transferring PD signal under pulse voltage than that made of the MnZn ferrite. Based on that， a statistical method is discussed to obtain different statistical parameters and charts. Characteristics of statistical parameters with the aging time， have been analyzed. In particular， a relation between the aging time and skewness of specimens is observed， and kurtosis and asymmetry of specimens for interturn insulation and grounding insulation embody different characteristics.