Partial discharge（PD）is one of the most effective means to characterize the insulation states of powerequipment. However

there are few studies on partial discharge characteristics of typical insulation defects in XLPEcables under DC voltage. Firstly

the mechanism of partial discharge of composite insulation under DC voltage isdeeply studied in this paper. And common types of defects and their causes in the XLPE cable are summarized.Three kinds of defect models are designed using XLPE cable and its prefabricated joints

including corona dis-charge

surface discharge at the stress cone

and air gap discharge at the insulation interface. The experiment is test-ed under step-wise DC voltage. Several typical features of different severity stages of the discharges are obtainedbased on the PD data measured by High frequency current method（HFCT）

including the three-dimensional map ofdischarge magnitude-time interval-discharge repetition rate

the scatter plots of previous discharge magnitude or pre-vious time interval with the current discharge magnitude. 28 fingerprint characteristics are obtained and a good recog-nition accuracy can be obtained based on the RBF neural network.