The invention provides an OLED pixel driving circuit and OLED display device. The OLED pixel driving circuit uses 5T1C structure and switch (K). By switch signal (Switch) controlling the switch (K) to connect first pin (K1) and second pin (K2) to enter display mode, and to connect first pin (K1) and third pin (K3) to enter sense mode, the ADC (ADC) senses the threshold voltage of the fourth TFT (T4), converted and used for data compensation in the display mode, able to compensate and eliminate the impact of threshold voltage of the fourth TFT (T4) on the current flowing through the OLED (D1); the light-emitting control signal (EM) controls the fifth TFT (T5) connected to the OLED (D1) to cut off during the data writing stage (t1) to keep the data signal voltage and the gate voltage of the fourth TFT (T4) unaffected by the OLED (D1) threshold voltage.