Polypropylene/elastomer composites are widely used in power cable insulation due to its excellent insulating properties and environmentally friendly characteristics. Enhancing water-tree resistance of polypropylene/elastomer composites is highly beneficial to long-term operational stability of power cable. The effect of EAA (ethylene acrylic acid copolymer) on water-tree resistance of PP/POE (polypropylene/ethylene-octene-copolymer) composites was investigated in this paper. Experiment results from the water blade electrode method demonstrate that blending EAA into POE markedly decreased the water-tree length of PP/POE composites. The polar functional groups through adding EAA can weaken the damaging effect of moisture on PP/POE composite. The DSC results show that the addition of EAA has no effect on the melting-crystallization temperature of PP/POE. Moreover, the addition of EAA slightly increase the power frequency breakdown field strength of PP/POE composite and has no significant negative impact on its power frequency dielectric loss. However, adding EAA will increase the conductivity of PP/POE and decrease its mechanical strength.