It is so easy for polyethylene to accumulate space charge that there is a problem of insulation deterioration and service life reduction for polyethylene insulated HVDC cable. In order to research the properties of space charge and conduction current of insulation materials under DC electric field, and taking the fact into account that for the same piece of samples, separate measurement results cannot be used for combined analysis strictly because of the displacement current component in external current, a new type of equipment based on pulse electro acoustic method (PEA) and the “same region time division” technique is designed to perform simultaneous measurement on plate specimen. The measurement results of space charge distribution and high electric field conduction in low density polyethylene (LDPE) plate sample are presented in this paper. The experimental results show that with the increase of electric field, increasing heterocharges around anode is accumulated, and the transition from heterocharges to homocharges around cathode can be observed. The phenomenon has relationship with impurity dissociation and different electrode materials. Displacement current density at room temperature under the condition of low electric field among the external current ratio is greater than that of the conduction current. The relationship between conduction current density and the electric field intensity also conforms to the Space Charge Limited Current theory.