Abstract: Substrate cultivation has been shown to positively influence both the yield and quality of tomatoes. Furthermore, biochar, recognized as a soil conditioner, exhibits characteristics such as abundant porosity and a large specific surface area, making it an ideal additive in the substrate. To clarify the effects of irrigation and fertilizer coupling on the yield and quality of tomato cultivated in biochar matrix, biochar was incorporated into a substrate mixture that included agricultural waste, such as distiller's grains and straw. A greenhouse experiment was conducted to investigate the effects of varying irrigation and fertilizer regimes on leaf area index (LAI), soil and plant analyzer development (SPAD), plant nutrient uptake, C/N ratio, N/K ratio, yield and quality of tomato cultivated in biochar substrate. The experiment consisted of two irrigation levels: I₁ (100% ET_c, where ET_c refers to crop evapotranspiration) and I₂ (80% ET_c); two fertilization rates (N-P₂O₅-K₂O): F₁ (240-180-200 kg/hm²) and F₂ (180-135-150 kg/hm²); and four amounts of biochar application: B₀ (0%), B₁ (1%), B₃ (3%), and B₅ (5%). Furthermore, a structural equation model (SEM) was utilized to explore the driving factors of water-fertilizer coupling on the yield and quality of tomatoes cultivated in biochar-enriched substrates. Additionally, an entropy weight-TOPSIS multi-objective comprehensive evaluation model was also constructed, targeting yield, quality, and their key driving factors, to identify the optimal scheme for coupling water and fertilizer with the biochar matrix. The results indicated that the biochar substrate significantly enhanced LAI, SPAD values, nutrient uptake, yield, and quality of tomatoes (P ＜ 0.05). Under the same conditions of irrigation and fertilization, the biochar matrix improved potassium absorption and carbon assimilation of the whole plant, yield, and vitamin C content in the tomato plants while simultaneously reducing nitrate content. Notably, the addition of 3% biochar resulted in a more pronounced increase in LAI, SPAD, nutrient uptake, yield, and quality of the tomatoes. Furthermore, under the same fertilization and biochar application, reductions in irrigation amount led to decreases in LAI, SPAD, fruit nitrogen uptake, fruit carbon assimilation, and carbon assimilation of the whole plant by 17%, 3%, 12%, 10%, and 8%, respectively. Conversely, the content of soluble solids, vitamin C, and soluble sugar exhibited increases of 17%, 8%, and 11%, respectively, with reduced irrigation. The SEM revealed that the carbon assimilation of the whole plant was the primary regulatory factor influencing yield, showing a significant positive correlation (λ=0.96, P＜0.001). The N/K ratio emerged as the principal regulatory factor affecting both nitrate content and the sugar-acid ratio, demonstrating a significant negative correlation with the sugar-acid ratio (λ=-0.66, P＜0.01) and a significant positive correlation with nitrate content (λ=0.53, P＜0.001). The SPAD value had an indirect promoting effect on yield and quality. Using the entropy weight-TOPSIS multi-objective comprehensive evaluation model, it is concluded that I1F2B3 treatment has the highest comprehensive ranking, and its relative closeness degree is 0.76, which is the optimal water and fertilizer and biochar matrix coupling management strategy for synergistically improving yield and quality. This research provides a theoretical basis for improving the utilization rate of agricultural waste and the scientific management of irrigation, fertilizer, and biochar in the cultivation of high-quality vegetables.