Abstract: A fiber optic two-way transmission system for video & data is designed by using wavelength division multiplexing(WDM) technology. The system, therefore, realizes to transmite one channel of video signals upstream and one channel of data signals downstream in a single mode fiber. In the design, the PFM (pulse frequency modulation) technology is used for video transmission, and the FSK (frequency shift key) technology is used for data transmission. The system can transmite signals of video & data longer than 100 kilometers without repeater.