Abstract: A Free Air CO₂ Enrichment (FACE) system for rice and winter wheat rotation was established, elevated CO₂ concentration was controlled to 200μmol·mol^-1 above ambient by computer system platform according to ambient CO₂ concentration variation, wind direction, wind speed, canopy height and day-night changing. Experiments showed that the main factors affecting control precision are wind speed, crop and soil respiration and thickness of diffuse layer. After parameters adjustment, in daytime the time fraction for control precision achieve 80% is 83%, in night is 68%. The CO₂ concentrations distribution in FACE rings are uniformity. The set CO₂ is 557mol·mol^-1 in daytime and 608 mol·mol^-1 in night.In2001 rice season the target achievement ratios(TAR) were 1.03 after sunrise and 1.09 after sunset, respectively.