This paper introduces the study on omni-directional vision system calibration method using central catadioptric projection property of space line. The catadioptric image point of space line was captured applied ray-tracing algorithm. A conic fitting algorithm based on least-square theory was raised which be used in catadioptric image fitting of line. System imaging parameter was determined by cholsky decomposition and omni-directional vision system was calibration. The calibration experiment on real omni-directional vision system verifies its effect. Keywords: omni-directional vision system; calibration; conics; fit; ray-tracing algorithm