A shift register circuit including a first shift register unit, a second shift register unit, a third shift register unit, and a fourth shift register unit connected in serial. The second shift register unit includes an output terminal, and a pull down system pulling the voltage of the output terminal of the second shift register unit according to a pull down signal. The fourth shift register unit includes a third switch and a fourth switch. The fourth switch has a control terminal electrically coupled to the second terminal of the third switch and the pull down unit. The fourth shift register unit generates the pull down signal according to the voltage level of the connecting point between the third switch and the fourth switch.
