Abstract: The effects of different supplemental light from light-emitting diode (LED) on the photosynthetic characteristics and yield of soybean(Jiyu47)were studied.The results showed that the diurnal variation curve of photosynthetic rate was changed from unimodal to multimodal by different supplementary light.Even though LED light could extend the photosynthesis time,increase the photosynthetic rate and enhance the photosynthetic capacity,it didn't obviously affect the intercellular CO2 concentration,stomatal conductance and transpiration rate.Compared with the other supplemental light,the blue light showed the highest positive effect on photosynthetic rate,chlorophyll content,plant height,stem width,and grain yield per plant in soybean.Therefore,the blue light should be an optimal supplementary light for the growth of soybean in greenhouse.