Organic light-emitting diodes (OLEDs) with a structure of indium-tin-oxide (ITO)/N, N'-bis (3-methylphenyl)-N, N'-diphenylbenzidine (TPD): polystyrene (PS)/tris (8-hydroxyquinoline)-aluminum (Alq3)/Mg: Ag were fabricated. Among them PS: TPD thin film acts as a hole transporting layer (HTL)and was prepared via dimethylbenzene solution dissolved with a mixture ofPS: TPD by spin-coating method. The influence of TPD dopde ratio in the mixture on the performance of device was investigated. Experimental results show that luminescent brightness of devices increase with the enhancement of TPD doped ratio, while electroluminescent spectra are not affected. In addition, lifetime of the device when the ratio of TPD to PS is 7: 3 was 4 times higher than that of pure-TPD device. This phenomenon was postulated that PS enhanced the uniformity of TPD film, which was characterized by the result of atomic force microscope (AFM)analysis, and thus overcame the shortcoming oflow stability of small-molecular film.