The present invention provides an OLED array substrate, a manufacturing method of the same, a display panel, and a display device, and relates to the field of active matrix organic light-emitting diode (AMOLED) display technology. The present invention can solve the problem that turn-on and turn-off of a switching thin film transistor and grayscale control cannot be performed effectively because the switching thin film transistor and a driving thin film transistor are manufactured as thin film transistors having same performance parameters in an existing OLED array substrate. The OLED array substrate according to the present invention includes a switching thin film transistor and a driving thin film transistor, wherein, an S factor of the switching thin film transistor is less than that of the driving thin film transistor.