An active touch pen includes a pen barrel, a pen head, a pen shaft, a sleeve, a processor, a sensor and a wireless transmission assembly. The pen head is connected to the pen barrel. The pen shaft and the sleeve are respectively disposed in the pen barrel, and the pen shaft penetrates through the sleeve. The processor, the sensor and the wireless transmission assembly are respectively connected to the pen shaft. The sensor is configured to detect variation of a first pattern of the sleeve during the sleeve rotating relative to the pen ban-el so as to obtain a first sensing data and transmits the first sensing data to the processor. The processor calculates rotation amount of the sleeve according to the first sensing data and transmits the rotation amount to the touch display device through the wireless transmission assembly.