Abstract: 【 Objective 】 This experiment aims to clarify the physiological response of tomato seedlings to supplemental lighting under sub-low temperature stress by studying the effects of supplemental lighting on tomato seedling growth and photosynthetic performance with a view of providing theoretical basis and technical support for the cultivation of strong tomato seedlings under such stress.【 Method 】 The experiment used the tomato variety 'Money Maker' as the material and employed regular Hoagland nutrient solution for regular quantitative irrigation, and applied white: blue (2∶1) compound light to treat tomato seedlings under sub-low temperature conditions of 15℃/8 (day/night) supplemental lighting. A total of four treatments were set, namely normal temperature without light treatment (CK), normal temperature with supplemental lighting (CK+USL), sub-low temperature stress (LT), sub-low temperature stress supplemental lighting (LT+USL).【 Result 】 Compared with the sub-low temperature stress, plant height and stem diameter of tomato plants increased significantly by 24.92% and 4.58%, respectively, and the fresh weight of leaves, stems, roots and total fresh weight increased significantly by 24.71%, 23.68%, 31.01% and 25.23%, respectively, total root length, surface area, total volume and projected area of tomato seedlings increased significantly by 25.73%, 29.31%, 25.93% and 14.22% , respectively. In addition, leaf net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) increased by 85.77%, 19.09% and 44.59%, respectively, while the intercellular carbon dioxide concentration (Ci) decreased by 15.60% after supplemental lighting under sub-low temperature.【 Conclusion 】 Under sub-low temperature stress, supplemental lighting of the leaves can significantly improve the photosynthetic performance of tomato seedlings, thus promoting robust growth of tomato seedlings.