The effect of graphene oxide (GO) modified by MoO_3as a hole injection layer is studied.The GO was prepared by using spin-coating method,then the bu ffer layer MoO_3was va cuum evaporated,and finally the composite film with high hole injection ab ility and transparency was obtained.The thicknesses of MoO_3are respectively 0nm,3nm,5nm and 8nm.When the thickness of MoO_3is 5nm,the composite fil m exhibits a transmission value of 88% at 550nm,and the organic light emitting diode (OLED) with the structure of indium tin oxide (ITO)/GO/MoO₃(5nm)/naphthyl-substituted benzidine derivativ e NPB,40nm)/Alq₃(40nm)/LiF(1nm)/Al(100nm) has the best performance.Then the OLED is further optim iz ed by changing the thickness of Alq₃.The thicknesses of Alq_3are 50nm,60n m and 70nm,respectively.By measuring the voltage,current,brightness,color coordinates,the electric light emission spectra and other parameters,it can be found that when the thickness of Alq_3is 50nm ,the device has the best performance.The OLED device with the structure of ITO/GO/MoO₃(5nm)/NPB(50nm) /Alq₃(50nm)/LiF(1nm)/Al(100nm) was prepare d.The maximum current efficiency of 5.87cd/A at the voltage of 10V is obtained,which is 50% higher t han that of the devices with GO as hole injection layer.