The all-optical information processing technology is the key technology in optical communication system. The all-optical 8-3 line encoder is the key device in all-optical signal processing. The all-optical 8-3 line encoder could be realized based on the cascade of OR gates.Using the cross phase modulation effect （XPM） based on semiconductor optical amplifier （SOA）， an all-optical OR gate was firstly designed and implemented， and then the all-optical 8-3 line encoder was designed.The feasibility of the designed all-optical OR gate and all-optical 8-3 line encoder was verified by using the OptiSystem photon simulation software. The all-optical 8-3 line encoder could be realized without the filter， so the design cost could be reduced， showing good application prospects in the future all-optical information processing.