The present invention provides a compensation method for the OVSS voltage drop of an OLED display device and a pixel driving circuit. According to the compensation method, a first pixel driving circuit for detecting the OVSS voltage is arranged in a part of sub-pixels of the OLED display device, and the OVSS voltages of the sub-pixels are detected by the first pixel driving circuit. Meanwhile, the detected OVSS voltages of the sub-pixels is adopted as a basis, and then the OVSS voltages of all sub-pixels of the OLED display device are obtained through the interpolation method. According to the OVSS voltages of all sub-pixels of the OLED display device, an OVSS voltage compensation look-up table is obtained. Finally, through the OVSS voltage compensation look-up table, the digital signal voltage is compensated. The compensated digital signal voltage is adopted to drive the OLED display device for displaying pictures. Therefore, the voltage drop of the OVSS voltage in the OLED display device can be effectively compensated, and the uniformity of the display brightness of the OLED display device is improved.