Abstract: A set of online detection system for chlorophyll fluorescence was designed. The fluorescence intensity of chlorophyll was detected by MINIPAM fluorescence detector， and LED light source were used as different light conditions， fluorescence parameters and fast response curves of plants under different conditions were measured. Detection system through 232 serial communication protocol with the host computer communication， WinControl software was used to achieve data collection and preservation. Experimental results showed that the suitable light could greatly promote the photosynthesis of plants， and thus improve the yield of crops， and the photosynthesis of plants under the environmental stress was obviously inhibited.

Key words: chlorophyll fluorescence, modulation fluorescence instrument, serial communication, programmable current source