In vegetable growing under protection, lack of carbon dioxide is one of the most important factors limiting photosynthesis. The application of 600-1200 mumol.mol-1 CO2 in the plastic house increased photosynthetic rates and ratio of C/N, promoted both vegetative and reproductive growth of bottle gourd plants. Plant height, stem diameter, leaf thickness and leaf area increased by 3.90-19.48%, 11.58-27.37%, 38.46-69.23% and 26.09-49.38%, respectively. Average single fruit weight and yield were 4.05-19.62% and 8.65-19.47% higher than that in normal air. Primary female flower position was lowered by 2.6-4.0. Net photosynthetic rate and the carboxylase activity of RuBP were greatest under CO2 1000 mumol.mol-1. The optimal concentration of CO2 applied to bottle gourd in spring was about 1000 mumol.mol-1.