Abstract: The effects of different concentrations of CO₂ on the growth and development of Flammulina velutipes are studied by controlling environmental conditions. It is shown that the optimal CO₂ concentration for the mycelial growth is 261.7～2930.5μmol/L, and the primordium formation of Flammulina velutipesis significantly inhibited by the increment of CO₂ concentration,the optimal CO₂ concentration of primordium formation is 12.3～60μmol/L. For attaining excellent quality fruit ofFlammulina velutipes,the range of CO₂ concentration in environment is 210～600μmol/L after fruit-body formation.