A pixel driving circuit of an organic light emitting diode (OLED) includes a first switch, a first capacitor, a transistor, a second switch, a second capacitor, and an OLED. The operation of the pixel driving circuit includes four stages of reset, threshold voltage compensation, data writing, and emitting. The pixel driving circuit compensates the threshold voltage of the transistor, so the driving current of the OLED is only related to the data voltage and the reference voltage.