The invention provides an OLED display device, using a 3T1C driving structure, and having the source of the first TFT to the reference voltage to ensure the second TFT to operate in saturation region in normal display state through controlling the reference voltage, to ensure the grayscale continuity. By using a reference voltage metal layer to cover all sub-pixels to replace reference voltage routing to provide reference voltage to the source of the first TFT, the invention eliminates the impact of reference voltage routing on pixel aperture ration.