Abstract: Abstract: Light emitting diode (LED) is a new light source which has several unique advantages, including the ability to control the spectral composition, the relatively cool emitting surfaces and minimum heating. Therefore, the research of precision utilization of LED is very important for energy saving and accuracy control in protected vegetable growth. In this study, Jinpeng NO.1 tomato seedlings were used as the material. After germination, the same-sized plants were selected and transplanted to the LED growth chamber with a temperature of 25℃ during the day and 20℃ during the night, 12 h photoperiod, and 65% relative humidity. In the daytime, tomato seedlings were grown under white LED at an illumination intensity of 168 μmol/(m2·s). The ratio of red light (655-665 nm) to far red light (725-735 nm) in white LED was 6.42. Before the tomato seedlings entered the darkness, they were shone by far-red light from 20:00 to 20:10 which lasted for 10 min. In the first part of this experiment, the effects of different end-of-day far-red light intensity on tomato seedlings height and stem fresh weight were studied. The end-of-day far-red light intensity included 0, 1, 2, 4, 6, 10 and 20 μmol/(m2·s). The results showed that, with the increase of far-red light intensity, the plant height and stem fresh weight increased, and when the far-red light intensity reached 10 μmol/(m2·s), the plant height and stem fresh weight reached their maximum value. In the second part of this experiment, the effects of end-of-day far-red light on tomato seedling morphology, dry mass distribution, hormone content, chlorophyll content, photosynthesis rate and mineral elements content were studied. The end-of day far-red light was scheduled to last for 10 min at an intensity of 10 μmol/(m2·s). The results showed that, after the end-of-day far-red light treatment, compared with the control, the plant height increased by 26.38%, the stem fresh weight increased by 15.36%, the dry mass was distributed more into stem, the content of IAA and GA3 in tomato leaves increased by 19.61% and 50.00% respectively, the content of IAA and GA3 in tomato stems increased by 42.18% and 40.00% respectively, and the content of chlorophyll and photosynthesis rate decreased by 20.24% and 13.99% respectively. The content of nitrogen (N) in stem decreased significantly, and the content of phosphorus (P) in leaf decreased significantly, while the content of potassium (K) in leaf increased significantly, and the N, P and K contents in root of tomato seedling all increased significantly (P<0.05). Phytochromes are important photoreceptors that sense red light and far-red light, and play very important role in plant growth and development. Phytochromes exist in 2 photo-interconvertible isomeric forms: the red-light-absorbing form and the far-red-light-absorbing form. After the end-of-day far-red light treatment, the far-red-light-absorbing form will quickly convert into the red-light-absorbing form, which affects the morphology of plant. Therefore, the height of tomato plants can be precisely controlled by regulating the end-of-day far-red light intensity.