This invention discloses an adaptive equalizer disposed on the front end of a receiver to improve the quality of a transmission signal comprising a data signal from a transmission cable. The signal compensation of the adaptive equalizer uses a long T as its observation unit when the transmission cable is idle, and uses a short T as its observation unit when the transmission cable is transmitting data signals. This invention further discloses a baseline wander compensator worked with the adaptive equalizer during the transmitting data period of the transmission cable. The disclosed adaptive equalizer can achieve its optimal processing effects.