Organic light-emitting Diode (OLED) emits light itself. It owns many advantages of optical-electronic characteristics as compared with Thin Films Transistor-Liquid Crystal Display (TFT-LCD). In order to achieve the requirement for full color flat panel display, the three primary colors which are red, green, blue (R,G,B) with high luminance¡Bhigh current efficiency¡Band high color purity are important study of research and development for OLED. In our experiment, the major materials are NPB¡BDPVBi¡BAlq3¡BLiF¡BPBD¡BDCJTB¡FThe materials of NPB¡BDPVBi¡BAlq3,LiF is used as hole transporting layer¡Bblue emission layer¡Belectron transporting layer, and electron injection layer, respectively. PBD is hole-blocking layer and DCJTB is red emission layer which is intended to indirectly demonstrate the hole-blocking effect in the interface between NPB and DPVBi layer. The blue light emission with short wavelength plays an important role in color conversion method (CCM) of full color technology. In the study, we improve and research on color purity of blue OLED by various thicknesses of organic layer. In addition, we research the influence of the device with different thicknesses of PBD layer as hole-blocking layer. In order to improve the color mixing phenomenon, we add extra DPVBi layer to the device with PBD layer. It can improve the blue color purity and obtain narrower full width at half maximum (FWHM).