Abstract: In order to improve the hydrogen production ability and light conversion efficiency of photosynthetic bacteria, , effects of light intensity on cumulative hydrogen production, hydrogen production rate and light conversion efficiency in the photohydrogen production from sorghum straw enzymatic hydrolysates within 48 h were investigated under the reaction temperature 30℃ and the mixed culture of photosynthetic bacteria inoculums 20%(volume fraction). The results showed that cumulative hydrogen production and hydrogen production rate increased with the increasing light intensity when it was lower than 5?000?lx, but decreased when it was higher than 5?000 lx. This phenomenon was similar with the light saturation point of plant, photoinhibition occurred when the light intensity were higher than light saturation point. The maximum influence coefficient of light increments occurred when the light intensity increased from 1?000 lx to 3?000 lx, which indicated the light intensity was more appropriate in this range from the point of light conversion efficiency.