With polyethylene oxide as a polymer additive, the composite films are prepared out of the solutions with different ratios of CH3NH3Br and PbBr2 (Ⅱ). The influences of different feeding ratios on the morphology, crystallinity, photophysics and electroluminescence properties of the films are studied. The effects of the species and contents of polymer additives are further investigated. The results show that the multilayer structure devices have the maximum luminance efficiency of 6.4 cd·A -1, much higher than that of the single-layer devices.