Abstract: We design and simulation a novel simplex optical communication system based on duo-binary code. Electrical-optical intensity modulation and duo-binary were adopted in the system. The results of software simulation showed that the single direction 20Gbit/s data was successfully transmitted over 20km SMF with = 5dBm power penalty, dispersion =17ps/nm/km, attenuation=0.2dB/km in the system. It has larger transmission capacity, lower BER and better transmission chromatic dispersion allowance than the common one.