Abstract: Photosynthesis is the most important chemical reactionon the earth. Light-induced delayed fluorescence(DF) in plants is an intrinsic label of the efficiency of charge separation at P680 in photosystemⅡ (PSⅡ). The intrinsic relationship between DF and photosynthesis was experimentally approved in this paper. The results showed that the DF excitation spectrum was obviously similar to the photosynthesis action spectrum; the DF signal changes with the intensity of excitation light source variation behaved as 'photoinhibition' phenomena of photosynthesis; and the DF intensity has an excellent correlation with photosynthesis rate at room temperature. Thus important experimental validations were provided to study plant photosynthesis by light-induced DF technology.