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Spread spectrum communication technology can effectively improve the anti-interference ability of the system, so it is widely used. As frequency band resources become more and more crowded, more and more attention is paid to M-ary spread spectrum because of its ability to balance bandwidth and transmission rate. Synchronization has always been the key technology in the M-ary spread Spectrum technology. System compares the error performance of the synchronous head synchronization method and the reference signal synchronization method. The soft digital method is used as the output of digital modulation and demodulation to the decoder. Based on the log-likelihood ratio, a suboptimal soft information extraction method suitable for M-ary spread spectrum system is proposed, and the influenced of hard decision and soft decision on the system is analyzed. The simulation results show that the error performance of the system is not significantly improved by the decision. When the convolutional coding is added, the error performance of the whole system is improved by the simulation parameter invariant analysis, which is about 5.2dB compared with that of the DSSS(Direct Sequence Spread Spectrum) system. Soft decision decoding has a gain of about 2dB over hard decision decoding. Considering the coding efficiency, the influence of soft decision and hard decision on the error performance of the system is analyzed separately . The results show that the error performance of the system is greatly gain compared with high signal-to-noise ratio. When the bit error rate , the soft decision decoding has about 0.7dB gain compared with the hard decision decoding . Soft decision decoding on the whole system error performance has 2.5dB gain.