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