Abstract: Solar greenhouses have been the main type of facility for tomato production in China. Low light in the facility is one of the most important restricting factors on tomato production, even leading to the decline of fruit quality and flavor. Phase supplementation can be expected to select the growth stage with strong sensitivity to low light. The low light intervention can be one of the economically feasible ways, in order to reduce the high cost of artificial light supplementation during the whole growth stage of tomato. This study aims to investigate the low light sensitivity of tomatoes at different growth stages. Tomato "Harvest 74-560RZ F1" was selected in a fully artificial light-based plant factory, where 1000 μmol/(m²·s) light was the control during the whole growth stage. Four treatments of low light were carried out at a certain period of time during the flowering, expanding, color turning, and harvesting stages. The low light intensity was 160 μmol/(m²·s). The light intensity of other growth periods remained at 1000 μmol/(m²·s) in the same treatment. The sensitivity of tomato quality formation to low light at different growth stages was clarified to analyze the accumulation of secondary metabolites that related to the tomato flavor and quality. Experimental conditions were all the same except for the light. The results showed as follows: 1) All low-light treatments decreased the contents of polyphenols, total flavonoids and lycopene. Among them, the total flavonoids and polyphenols contents of tomato were the lowest under low light treatment at the flowering stage among the treatments, which were significantly reduced by 35% and 29%, respectively, compared with the control (P<0.05). The lycopene content was lower under low light treatments at flowering and color-turning stages, which was significantly reduced by 45% and 60%, respectively, compared with the control (P<0.05). Lycopene was significantly and positively correlated with the total flavonoids and polyphenols content in tomato fruits under all treatments. 2) All low-light treatments significantly reduced the total amount and total content of volatile secondary metabolites, such as aldehydes, ketones, esters, hydrocarbons, and alcohols in tomato fruits (P<0.05). The highest and lowest contents were Aldehydes and alcohols under all treatments, respectively. The low light treatment at the expanding stage had the lowest total number of volatile compounds (40 species, 9% less than the control), while the lowest total content of volatile compounds was 28% less than the control at the flowering stage. Among them, the contents of aldehydes, esters and other volatile compounds were the lowest at flowering treatment, which was significantly reduced by 31.7%, 64.1% and 56.8%, respectively, compared with the control. The content of alcohols in tomato fruits was lower than that of other treatments under low light treatments at flowering and expanding stages, which was significantly reduced by 25.3% and 28.2%, respectively, compared with the control (P<0.05). Therefore, the low light stress at the flowering stage presented the greatest adverse effect on the accumulation of secondary metabolites related to fruit quality and flavor in tomatoes. The low light-sensitive stage of tomato flowering is required to be supplemented with artificial light sources. The intensity and quality of supplemental light can also be further investigated at the flowering stage, according to the expected performance and cost of supplemental light.