The disclosure provides an active stylus pen and signal transmission methods for the active stylus pen and a touch panel. The stylus has a touch module, a switching module, a signal comparison module, a control module and a pressure sensing module. The stylus determines a first signal generated by a touch panel, and compares an intensity of the first signal and a reference value through a first transmission path. When the intensity of the first signal exceeds the reference value, the stylus outputs a second signal to the touch panel. After the stylus outputs the second signal to the touch panel, the stylus switches to a second transmission path from the first transmission path. The stylus outputs a header signal to the touch panel. When determining a first time sequential distribution, the stylus outputs at least one bit of a pressure signal according to a second time sequential distribution.