Abstract: To clarify the effects of silicon fertilizer and photosynthetic bacteria on tomato growth in greenhouses under low light, the ‘Zhongza 9’ tomato variety was used as the experimental material. A substrate cultivation model was adopted, and a shade net was used to simulate a weak-light environment. Exogenous applications of 1.5 mmol·L⁻¹ sodium silicate and photosynthetic bacteria at a 75-fold dilution were applied singly and in combination. Five experimental treatments were set up: normal light (CK), low light (LL), low light + silicon (LS), low light + photosynthetic bacteria (LP), and low light + silicon + photosynthetic bacteria (LPS). The tomato growth and physiological characteristics, and the substrate physicochemical properties under different treatments were investigated to provide a theoretical basis for the application of silicon fertilizer and photosynthetic bacteria to alleviate low light stress in facility-grown tomatoes. The results showed the following: 1) Under LL treatment, the pH and activities of sucrase, urease, (neutral, and alkaline) phosphatase, and catalase of substrate significantly decreased compared to CK treatment, whereas the EC and thecontents of available P, available K, organic matter, total N, and total P significantly increased by 12.21% to 227.32%. Compared to LL treatment, LS, LP, and LPS treatments increased the activities of sucrase, neutral and alkaline phosphatase, and catalase, among which LPS treatment had the best effect, with enzyme activities increasing significantly by more than 30%. 2) Under the LL treatment, the accumulation of dry matter in both shoot and root of the plants significantly decreased; LS, LP, and LPS treatments all significantly increased the dry matter accumulation of tomatoes, significantly improving the robust seedling index by more than 40% and balancing the growth of the shoot and root. 3) Under the LL treatment, the content of photosynthetic pigments in tomato plants significantly increased, the chlorophyll a/b ratio significantly decreased, and the net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, and transpiration rate significantly decreased. Compared with the LL treatment, the LS, LP, and LPS treatments increased the chlorophyll b content in tomato plants, and the net photosynthetic rate significantly increased by more than 40%. 4) Under the LL treatment, the absorption of N, Ca, and Mg in the shoot of tomatoes significantly increased compared to that under CK treatment, whereas the absorption of P, K, and trace elements in th shoot of tomatoes, as well as the accumulation of all elements in the whole plants, were significantly inhibited. Compared with LL treatment, tomato plants treated with LS, LP, and LPS treatments had been certainly promoted on the absorption of most of the macronutrients and trace elements in tomato plants, with LPS treatment showing the best promoting effect. 5) The results of the RDA showed that under low light conditions, the substrate pH and the content of available nitrogen have a positive impact on the establishment of the root system morphology of tomato seedlings. Meanwhile, the root system morphology is positively correlated with the biomass accumulation of tomato seedlings, and negatively correlated with the plant height and internode distance. Principal component analysis of 19 indices, including tomato morphological parameters and mineral elements, showed that the comprehensive ranking of each treatment was as follows: CK> LPS> LP> LS> LL. In summary, the application of a mixture of 1.5 mmol·L⁻¹ sodium silicate and photosynthetic bacteria at a 75-fold dilution resulted in varying degrees of increased substrate enzyme activity, significantly improved growth conditions of both the shoot and root of the tomato plants, and simultaneously enhanced the absorption and utilization of mineral elements of tomatoes.