The use of common processors for signal processing has the advantages of flexibility, extensibility, and maintainability, and is one of the trends of future software radio development. This paper proposes a parallel high-speed quadrature phase shift keying (QPSK) demodulation method based on data decomposition. This method decomposes serial signal flow into signal blocks, then high-speed QPSK demodulation is achieved by parallel processing of multiple signal blocks. In order to eliminate the dependence of signal blocks processing, an open loop demodulation algorithm based on three-dimensional iterative search is proposed. In order to eliminate the phase ambiguity between the demodulation of each signal block, an ambiguity consistency method based on data redundancy is proposed. The simulation results show that the signal-to-noise ratio loss of the parallel demodulation method is less than 0.1 dB. The demodulation system is built on the HP Z820 workstation, and the demodulation information rate is 1 154.2 Mbps.