An active touch pen, a touch input system and a method of driving the same are provided. The active touch pen includes a pen tip and a pen body, where a control circuit and a signal supply circuit are in the pen body. The control circuit is configured to detect a detection parameter value corresponding to an inclination angle of the pen body, and adjust, according to the detection parameter value, a signal amplitude of an output signal supplied by the signal supply circuit; an input end of the signal supply circuit is connected to an output end of the control circuit, to supply the output signal through the pen tip.