Abstract: In order to clarify the physiological response and demand pattern of greenhouse tomatoes to CO₂,“Meihong 2”was used as the experimental material to measure the flowering yield,fruit number per plant,fruit weight,sugar content,acid content,and vitamin C content of tomatoes after adding600,900,and 1 200 mg/kg of CO₂.The results showed that increasing CO₂application could increase tomato flowering by 25% to 50%,and increase the number of fruiting per plant,and increase yield by28.29% to 51.04%,but had no effect on the average fruit weight.Compared with the control,after 20days of adding CO₂,the sugar contents of the fruits treated with 600,900,and 1 200 mg/kg were5.27,5.49,and 5.65 g/kg,respectively,significantly higher than the sugar content of 4.71 g/kg in the control.The acid contents were 2.48,2.23,and 2.02 g/kg,respectively,significantly lower than the acid content of 3.03 g/kg in the control area.The vitamin C contents were 356.38,420.38,and 348.38 mg/kg,respectively,significantly higher than the control area′s 260.88 mg/kg content.Among them,the 900 mg/kg treatment had the best effect on improving vitamin C.Thus,adding CO₂in a greenhouse could not only increase tomato yield but also effectively improve tomato quality.The appropriate dosage was 900 mg/kg.