The present disclosure relates to a backlight source, a display device, and a driving method thereof, in the field of field of displays. The backlight source includes a Passive Matrix Organic Light Emitting Diode (PMOLED) display device, wherein the PMOLED display device includes a transparent substrate. A transparent wiring layer, an anode layer, a light emitting layer, a transparent cathode layer, and a transparent pixel definition layer are arranged on the transparent substrate subsequently. The light emitting layer includes a plurality of light emitting units for emitting white light, and the plurality of light emitting units are arranged in an array. The anode layer includes a plurality of anodes, the plurality of anodes are arranged below the corresponding plurality of light emitting units respectively, and can reflect light emitted from the corresponding light emitting units. The backlight source in the present application is implemented with PMOLED display device. The substrate, wiring layer, cathode layer and pixel definition layer of the PMOLED display device can use transparent materials, resulting in high transmittance of the backlight sources in the areas excluding the anodes, such that the transparent display device can have high transmittance.