In this study, tomato variety ‘Jinpeng M6’ was used as the material and pot experiments were conducted to study the effects of different amounts of fulvic acid on tomato growth, nutrient absorption, carbon and nitrogen metabolism, and yield and quality. The results showed that the dosage of fulvic acid at 30 mg/kg could promote the growth of tomato plants at the seedling stage, increase the root volume and surface area, promote the absorption of nitrogen, phosphorus and potassium, and increase the content of soluble protein, soluble sugar and glutamine synthase, and the indexes of tomato reached the highest value. Compared with the control (fulvic acid was not applied), soluble sugar and vitamin C in tomato increased by 43.9% and 35.4%, respectively, and tomato yield increased by 28.1%. When the amount of fulvic acid was 3000 mg/kg, there was no significant difference of tomato-related indexes between the treatment and the control. Based on material cost and various indexes, the optimal dosage of fulvic acid is 30 mg/kg.