There is provided a signal demodulating method of a two-phase frequency shift keying (FSK) digital demodulator. The method utilizes at least a detect circuit respectively detecting and collecting a positive edge signal and a negative edge signal of an intermediate frequency signal. Then, two n-bit ripple counters are utilized to refer to a threshold value and then receiving the positive and negative edge signal as a switch signal to reset the threshold value as an initial value of counters so as to start to count and compare to output a positive edge data bit and a negative edge data bit. Last, a hard decision logic circuit is used to perform a frequency-descending decision in accordance with the positive and negative edge data bit so as to send a base frequency signal. The method can decrease the logic gate counts, shorten the signal delay time, and increase the resolution of the demodulation. The present invention allows for; easy and practical signal demodulating method results, which can match the compact trend of the wireless products.