An adaptive equalizer apparatus with digital eye-opening monitor unit and the method thereof are provided. The apparatus comprises an equalizer unit, a sampling unit, and an eye-opening monitor unit. The equalizer unit equalizes a first signal to a second signal. The sampling unit over-samples the second signal and determines the logic status of the second signal according to the sampling data. The eye-opening monitor unit processes the sampling data and outputs a detecting signal according to the processing result. The detecting signal represents the adequacy of the parameters of the equalizer unit, and the equalizer unit determines whether to change its parameters according to the detecting signal.