The normal receivers of DSSS system despread and demodulate the IF signal separately, their process-gains are the period of the pseudo-noise sequence. But these process-gains usually cannot satisfy a low bit-error-rate if the signal-noise-ratio of input signal is very low. In a DSSS system based on the software radio, the receiver can despread and demodulate the IF signal simultaneously. It can be proved that this method can get a higher process-gain when the sample rate meets a certain condition, so it can be used in a low signal-noise ratio system.