This paper deals with the experimental study on the correlation between insulation resistance (R) and direct current (DC) component (idc) and corresponding aging degree of insulation in the course of the aging within cross linked polyethylene (XLPE)insulation. The aging tests were performed on a section of 10 kV transmission XLPE cable by means of water needle method, and R was measured by DC voltage superimposed method. R and idc were found to be significantly dependent on the corresponding aging degree of insulation in the course of aging of XLPE, and different kind of aging stage has different characteristics. Beside, there are generally similar regularity but different amplitude in the course of aging of XLPE insulation in different electrolyte, and the various electrochemical tree were found on the surface of aging XLPE cable immersed in CuSO4 solution. Therefore, according to the changing regularity of the DC characteristic parameters i.e. R and idc within XLPE insulation judging the aging degree of XLPE insulation will be an effective method.