Six models of typical insulation defects are designed and lab-simulated system used for partial discharge (PD) detection of cables and accessories has been constructed to study PD characteristics of internal insulation defects in 110 kV XLPE cable system. By employing CPDM, a kind of on-line PD detector, test data of various models including related PD diagrams are obtained for our research. Based on these characteristic parameters, discharge characteristic analyses of a single PD pulse are presented and statistical operators can be obtained by numerical calculation. The experimental results show that CPDM on-line detecting method is effective for detecting PD signals from internal defects of cable accessories. In addition, there are significant differences in the some statistical parameters (e.g. discharge phase, discharge repetition rate, etc) and characteristic parameters of time-domain PD waveform which can be used as reference points for PD patterns identification in future research.