An active pen for a touch display screen, a touch input system, a method for driving an active pen, and a method for driving a touch input system are provided. The active pen includes: a signal receiving device, a processor which is in signal connection with the signal receiving device, and a signal transmitting device which is in signal connection with the processor. The signal receiving device is configured to receive a first coupling voltage between the active pen and the touch display screen. The processor is configured to process the first coupling voltage to obtain a second coupling voltage, and a polarity of the second coupling voltage is opposite to a polarity of the first coupling voltage. The signal transmitting deice is configured to transmit the second coupling voltage to the touch display screen.