A half duplex device and signal processing method thereof. First, a signal detection unit of a signal detector of a half duplex device obtains a short-term power and long-term power. Next, a data update unit of the signal detector sets a short-term power threshold as a default threshold, determines whether the long-term power is greater than the default threshold, sets the short-term power threshold value equal to the long-term power value if the long-term power value is greater than the default threshold value, and provides smooth performance in a noisy environment.