Abstract: Conventional high nitrogen (N) application practices in drip-irrigated processing tomato (Solanum lycopersicum L.) production in Xinjiang, China, are associated with low nitrogen use efficiency (NUE) and pose significant environmental pollution risks. To address this issue, this study investigated the potential of fulvic acid (FA) application to mitigate these negative impacts under the prevailing high N regime. The specific objectives were to evaluate the effects of different FA application rates on the soil-crop continuum and to identify the optimal FA rate for enhancing tomato yield, quality, and NUE. A field experiment was conducted over two consecutive growing seasons (2023 and 2024). Five fulvic acid application rates were tested: CK (0), FA1 (10 kg/hm²), FA2 (25 kg/hm²), FA3 (50 kg/hm²), and FA4 (75 kg/hm²). All treatments received the same conventional high rate of nitrogen fertilizer. The study comprehensively assessed the impacts of FA on: (1) Soil properties: Nitrate-N (NO₃^--N), ammonium-N (NH₄⁺-N), total nitrogen (TN), and total carbon (TC) content in the 0～60 cm soil profile. (2) Crop growth and physiology: Plant height, stem diameter, leaf area index (LAI), aboveground biomass, leaf SPAD (soil and plant analyzer development) value (indicating chlorophyll content), and photosynthetic performance. (3) Yield and water use efficiency: Processing tomato fruit yield and irrigation water use efficiency (IWUE). (4) Fruit quality: soluble sugar, soluble solids, organic acid, vitamin C content, lycopene content and sugar acid ratio. (5) Nitrogen dynamics: Plant N uptake efficiency, aboveground N accumulation, partial factor productivity of nitrogen (PFPN), and N surplus within the soil-crop system. A total of 16 key indicators spanning these categories were measured. To integrate these multifaceted results and determine the optimal FA application rate, a comprehensive evaluation model was constructed using both the Analytic Hierarchy Process (AHP) and Principal Component Analysis (PCA). FA application significantly increased (P<0.05) the concentrations of NO₃^--N, NH₄⁺-N, TN, and TC within the 0～60 cm soil layer compared to the CK control. Significant improvements (P<0.05) were observed in plant height, stem diameter, LAI, aboveground biomass, leaf SPAD value, and photosynthetic parameters in FA-amended plots relative to CK. Compared to CK treatment, FA3 and FA4 treatments significantly increased processing tomato yield by 8.39%～16.33% and irrigation water use efficiency by 8.39%～16.32%. At the same time, soluble sugar, soluble solids, fruit vitamin C, lycopene content, and sugar acid ratio quality parameters have also been improved to varying degrees. In addition, compared with CK treatment, FA3 and FA4 treatments significantly increased plant nitrogen uptake efficiency, aboveground nitrogen accumulation, and nitrogen partial factor productivity, and reduced nitrogen surplus in the soil-crop system by 9.93%～10.67% (2023) and 7.20%～7.67% (2024) (P<0.05). The comprehensive evaluation model, integrating the 16 indicators through AHP and PCA, consistently identified the FA3 treatment (50 kg/hm²) as the optimal fulvic acid application rate under the conventional high N regime. This study demonstrates that supplementing conventional high nitrogen fertilization with fulvic acid, particularly at the optimal rate of 50 kg/hm², is a highly effective strategy for Xinjiang's drip-irrigated processing tomato production. FA application significantly improves soil nitrogen and carbon status, enhances crop growth and physiological performance, boosts yield and irrigation water productivity, improves key fruit quality attributes, and promotes more efficient nitrogen utilization, thereby substantially reducing the risk of nitrogen loss and environmental pollution. These findings provide a robust theoretical foundation and practical solution for achieving the dual goals of increasing yield and quality while enhancing nitrogen use efficiency in processing tomato cultivation in Xinjiang.