The invention provides an OLED display device array substrate preparation method. Doping of different function regions such as a channel region, a source region, a drain region, an LDD region and a capacitor lower pole plate is realized through two masks and three ion doping steps, the preparation requires fewer steps, and the process is simple. The three doping steps are implemented under the condition of spacing by a gate insulation layer, the same accelerating voltage can be applied, the process cost is saved, and the stability of the process and the yield of devices are improved. The accelerating voltage is the same, and a rapid thermal treatment process is not needed after the completion of the doping process, thus simplifying the process steps. A whole semiconductor layer is doped before the semiconductor layer is patterned, and after a TFT is formed, the carrier mobility of the TFT channel region is increased, a small drift value is given to the threshold voltage (Vth), the space heterogeneity and instability of the TFT are compensated successfully, and the brightness (gray) of pixels can be accurately controlled by controlling the magnitude of current of each pixel unit.