Disclosed is a demapping method of a soft-decision of an efficient soft determining scheme which is applicable to a DVB-2 satellite communication system. The soft-decision demapping method for a digital signal received through a transmission channel in a communication system using a phase shift keying (PSK) scheme includes: selecting reference symbols in an area having a higher probability than a predetermined probability that the received signal will be positioned among all reference symbols on a constellation diagram using a most significant bit (MSB) value of the received signal; and acquiring a maximum value of a log likelihood ratio (LLR) for the selected reference symbols.