Polymer solar cells with polyethylene glycol (PEG) cathode buffer laye r formed by PEG migration were prepared,and the photoelectric performance of polymer solar cells was stud ied in this paper.The X-ray photoelectron spectroscopy (XPS) results indicate that PEG migrates from active layer to the interface between the active layer and Al electrode and forms a cathode buffer layer.The results of ultraviolet-v isible absorption spectra,current density-voltage (J-V) characteristic curves and extern al quantum efficiency spectra show that the formed PEG buffer layer improves the interfacial contact and reduces the energy barrier between ac tive layer and electrode,thus improves the photoelectric performance of the polymer solar cell significantly, and the short circuit current density (J_sc), open circuit voltage(Voc) and fill factor (FF) are all enhanced obviously.The polymer sol ar cell with 0.5% (volume percentage) PEG doped into P3HT:PCBM active layer gives the maximum power conversion efficiency (PCE) of 3.07%,which is enhanced by 38.5% compared with the de vice without PEG.