It has been known that the ethylene propylene rubber（EPR） is widely used in MV/HV power cables which are strongly affected by the formation and movement of space charge in their insulation layer. In this paper

the space charge distribution of EPR under different DC electric field is measured by using pulsed electro-acoustic（PEA） method for revealing the formation mechanism and characteristics of space charge in EPR. The results show that the homo-charge injection occurs under the electrical field strength more than 2.5 kV/mm. The total charge quantity is increased with the rise of electric field. The formation process of the space charge in EPR during polarization can be divided into four stages:（Ⅰ） no charge injection

（Ⅱ） bipolar injection

（Ⅲ） charge transformation and recombination

and（Ⅳ） anode injection. When the DC voltage is removed

the dissipation of the space charge is affected by the depth and density of traps in EPR. The electric field inside EPR samples is distorted by the positive space charge packet under high electric field strength

which may affect the insulation aging and the breakdown voltage.