Green organic light-emitting devices with a structure of indium-tin-oxide (ITO)/polystyrene (PS):N,N9-bis-(3-naphthyl)-N,N9-biphenyl-(1,19-biphenyl)-4,49-diamine (NPB)/tris-(8-hydroxyquinoline)-aluminum (Alq3)/Mg:Ag were fabricated. A doping system consisting of small-molecular hole transporting material NPB and polymeric matrix PS was applied as a composite hole transporting layer (HTL), and the thin film preparation was simplified via spin-coating technique. By adjusting the component ratio of the doping system, several devices with different concentration proportion of PS:NPB are constructed. The electroluminescent characteristics of the devices were investigated and discussed. This study demonstrated that the difference of doping concentration of NPB has a remarkable impact on the optoelectronic performance of both HTL and the devices. Optimum device performance can be obtained by choosing a suitable concentration proportion of PS:NPB at 1:1. This study contributes to the construction of composite functional layers of organic light-emitting diode (OLED) devices and to the technical modification.