The present disclosure provides a pixel circuit, its driving method, an OLED display panel and an OLED display device. The pixel circuit includes row pixel units each including subpixel units. The row pixel unit includes an auxiliary compensating circuit, which is configured to generate a switching control signal inputted to a subpixel driving circuit according to a scanning signal from a gate driving circuit, and generate a compensating control signal inputted to the subpixel driving circuit according to a control signal from the gate driving circuit. The subpixel driving circuit is configured to receive a data voltage from a data line accordance to the switching control signal, control a driving transistor to drive an OLED to emit light according to the data voltage, and compensate for a threshold voltage of the driving transistor according to the compensating control signal when the driving transistor drives the OLED to emit light.