Abstract: Taking rice "green drought 639" as research object, far-red irradiation was radiated at seed stage（T₁）, bud stage（T₂）and seedling stage（T₃）, and a control group（CK）was set．Physiological indicators, growth characteristics, and water use efficiency of rice seedlings were calculated, influence of far-red light on growth and water use efficiency of rice seedlings was studied．Results showed that, leaf area of rice seedlings irradiated during seed stage increased by 15.82% and 20.46% compared to bud and seedling stages, respectively．Relative growth rate of rice seedlings irradiated during bud stage increased by 23.10% and 37.01% compared to seed and seedling stages, respectively．Growth amplitude of root length, root crown ratio, net assimilation rate and other indicators was greater than that of irradiation during seed and seedling stages．Water use efficiency of rice seedlings irradiated during seedling stage increased by 16.60% and 23.07% compared to seed and bud stages, respectively．In conclusion, far-red light irradiation during bud stage of rice seedlings can effectively promote growth of rice seedlings．Far-red light irradiation at seedling stage of rice seedlings can significantly improve water use efficiency of rice seedlings．This research provides a reference for improving water use efficiency of rice and other crops from perspective of optical agriculture．