Abstract: Tomatoes are rich in dietary fiber. High hydrostatic pressure (HHP), combined with ultra-high pressure homogenization (UHPH) technology, can further increase the content of soluble dietary fiber (SDF) in tomato juice, thereby enhancing its nutritional value. This study used whole tomatoes as raw material and modified tomato juice through high-pressure processing⁺ (HPP⁺). The SDF extraction yield was used as an indicator, with HHP pressure, HHP time, and UHPH pressure as the factors under investigation. Single-factor and response surface experiments were conducted to optimize the processing conditions and determine the best modification process. The structural changes before and after modification were detected by field emission scanning electron microscopy, particle size, and infrared spectroscopy. The results showed that under the conditions of HHP pressure at 500 MPa, HHP treatment time of 15 minutes, and UHPH pressure at 200 MPa, the SDF extraction rate of tomatoes was the highest at 11.35%±0.25%, compared to 6.21%±0.10% for the unmodified sample. Moreover, compared to the unmodified SDF, the structure of the modified tomato SDF became more porous, with a multi-porous surface structure, the average particle size decreases from 977.34 nm to 645.48 nm. The hydrogen bonds within SDF molecules were broken, the content of uronic acids was reduced, and the monosaccharide composition changed. In summary, processing tomatoes with HPP⁺ technology could effectively enhance SDF content (P<0.05) and alter the SDF structure. This study provides a theoretical basis for the green processing of tomato juice in the food industry.