In order to obtain the characteristic parameters of dampness status of resin impregnated paper (RIP),the time domain dielectric response technique is performed on the dampness status evaluation,and the RIP moisture contents are intensively studied based on polarization and depolarization current (PDC) method. Firstly,RIP insulation samples with different moisture contents are prepared in the laboratory and the PDC curves are measured. Then,the optimization algorithm combining genetic algorithm and interior point method is introduced,and the parameters of extended Debye model are obtained by Matlab simulation. Finally,two characteristic parameters of dampness status are extracted,which are the relaxation contribution coefficient of the maximum time constant branch A₉ and the stable depolarization charge quantity Q_d-5000. Conclusions from the research results are as follows. The PDC curve moves upward as the moisture content increases. The dampness of the RIP insulation results in the increase of its conductivity and the decrease of its insulation resistance，absorption ratio andpolarization index. The parameters of the 9-branch extended Debye model are sensitive to the RIP insulation dampness status,and the A₉ shows a linear relationship with moisture content. The depolarization charge quantity is sensitive to moisture content,and the Q_d-5000 shows an exponential relationship with moisture content.