Abstract: Three methods for CO₂ enrichment-chemical reaction(H₂SO₄+NH₄HCO₃), briquet combustion, granular CO₂ fertilizer were comparatively studied in free tunnels and solar greenhouses for cucumber cultivation, and the yearly total cost of different methods(including pure liquid CO₂) were compared. Chemical reaction had higher CO₂ releasing velocity and relatively lower equipment depreciation charge; honeycomb briquet combustion produced CO₂ at moderate rate, and the raw material cost was the least; granular CO₂ fertilizer having highest raw material cost released CO₂ slowest. When the re-use of by-product of chemical reaction was concerned, annual cost of chemical reaction was similar with that of briquet combustion and liquid CO₂. Comprehensively evaluated from viewpoints of ecology, energy-saving, cost and effect, briquet combustion was in more accordance with the present situations in China including facility type, economic situation, resource condition and technique level, and so on.