An organic light emitting diode (OLED) display panel and a driving method thereof are provided. The OLED display panel includes a plurality of pixel unit circuits and an external compensation unit connected to all of the pixel unit circuits. The external compensation unit performs external compensation on each of the pixel unit circuits, obtains an initial threshold voltage of a corresponding driving thin film transistor (TFT) of each of the pixel unit circuits, adds the initial threshold voltage to a predetermined initial potential, and then inputs a sum of the initial threshold voltage and the predetermined initial potential to each of the pixel unit circuits Each of the pixel unit circuits performs internal compensation based on the sum of the initial threshold voltage and the predetermined initial potential.