The present invention provides a signal processing device and a signal processing method utilized in a communication system, wherein the communication system includes at least a channel. The signal processing device includes an analog-to-digital converter (ADC), a first adding unit, a feed forward equalizing unit, a data slicing unit, a second adding unit, an infinite impulse response (IIR) compensating unit, and an interference eliminating unit. The signal processing device and the signal processing method thereof disclosed in the present invention can utilize the IIR compensating unit to solve an error distortion problem in the communication system so as to improve the whole efficiency.