A data slicer with a source-degeneration structure is described. In particular, this invention can be implemented in a FM demodulation system. It located at the end of the demodulator. The data slicer can slice a signal transmitted through air and demodulates the same with a demodulator to produce a frequency-shifted modulation (FSK) signal. The signal is a perfect square-wave and is transmitted to a base band circuit. The data slicer with a source-degeneration structure obtains the exact reference voltage. The reference voltage is not affected by noise and doesn't need the coupling capacitor, so it can reduce the difficulty of manufacture and cost. The present invention has a common-source unit with a source-degeneration resistor for producing an input signal and a reference voltage, and a comparator unit for comparing the input signal and the reference voltage and outputting a square-wave signal that corresponds to the input signal.