Abstract: This paper focuses on the optimal combining of multiple multi-path fading signals. Diversity is a classical technology combating the multi-path fading. The maximum ratio combining is the optimal combining schemes. Real weights are used for multi-path signals combining in the traditional diversity system. This may not make all frequencies in the spectrum of combined signal to achieve maximum signal-to-noise ratio. Based on the best combining structure of multi-path fading signals, a sub-band combining algorithm is proposed in this paper. The cosine modulated filter banks are used to divide the width band fading signals into several narrowband sub-signals. Optimal combining of corresponding sub-band signals and perfect reconstruction techniques make the optimal combined output signal. Simulation results show that the sub-band combining algorithm can effectively improve the quality of the demodulation of the combined signal. And it evidently reduces the symbol error rate of combined signal.