A theoretical model based on a novel experiment scheme of dual-channel optical chaotic communication has been presented, and is proved to be reasonable by comparing the numerical simulations with the experimental results. After deducing the transmission function of semiconductor laser by small-signal analysis, how to reasonably select the system parameters has been given in order to realize the effective transmission of signal. Moreover, the cross talk between two channels has been analyzed quantitatively. For a 250MHz modulation message, the numerical simulation shows that it can be hidden efficiently during the transmission and decoded easily in the receiver.