Polymer light-emitting diodes(PLEDs) devices based on MEH-PPV were fabricated. The performance of PLEDs device with inserting insulating layer PEO nserted between the metal cathode and emissive polymer was enhanced. Furthermore, when cathode Al was modified by PEO/LiF, the threshold, the luminescence intensity, the efficiency and stability of the device were improved significantly. Experiment results show that the improvement of the device performance is caused by the introduction of PEO. The PEO between the metal cathode and emissive polymer works as the carrier barrier for carriers, and the injection of holes is restrained by the accumulation of holes on the surface. Meanwhile, electron injection is enhanced, and the dissociation of exciton is reduced.