Abstract: Tomato is one of the most important economic crops with the largest facility cultivation area in China. Among them, the multi-span greenhouse has dominated in the efficient production of tomato cultivation. However, the stress of weak light has limited to the high-quality production of tomatoes in the multi-span greenhouses in recent years. Therefore, this study aims to explore the effects of the foliar application of DCPTA, inositol application in the root zone, and their combined application on the tomato plant growth, fruit quality, and root-zone liquid properties under year-round production. The tomato was also taken from the multi-span greenhouse. Four treatments were carried out: the CK (control), DC (foliar spray with 75 mg/L DCPTA), JC (nutrient solution with 50 mg/L inositol) and DC+JC (combined treatment). The quality of tomato fruit was evaluated using Total Quality Index (TQI), including the soluble solids, vitamin C, organic acids, soluble sugars, and the sugar-acid ratio. The findings were as follows. 1) The DCPTA and inositol shared a stronger performance to improve the quality under weak light conditions. There was a significant synergistic effect of the combined application. Specifically, the DC treatment was significantly enhanced the soluble solids in the early fruit stage, while the vitamin C and the sugar-acid ratio at the final fruit stage, compared with the CK; The JC treatment was significantly improved the soluble solids in the early fruit stage, while the vitamin C, soluble solids, and the sugar-acid ratio at the final fruit stage; The DC+JC treatment significantly increased the soluble solids and soluble sugars in the early fruit stage, while the soluble sugars in the peak fruit stage, and the vitamin C, soluble solids, soluble sugars, and the sugar-acid ratio at the final fruit stage. The JC treatment also increased the TQI in the early fruit stage by 18.18%, while the DC+JC treatment increased the TQI in the early and final fruit stages by 40.91% and 82.12%, respectively. 2) The DCPTA and inositol were effectively improved the nutrient absorption in the tomato plants. But there was no significant synergistic effect on the overall absorption of nutrients. Specifically, the DC, JC, and DC+JC treatments were significantly promoted the absorption of N, P, and Zn by the whole plant, compared with the CK. Additionally, the DC+JC treatment shared the significantly higher absorption of Mo and Mn in the stem, while the Cu and Fe in the fruit, compared with the DC or JC treatments. There was a more significantly synergistic effect, when both DCPTA and inositol were applied together. Furthermore, all DC, JC, and DC+JC treatments were significantly promoted the overall absorption of nutrients in the stem, compared with the CK. 3) The inositol was utilized to stabilize the root-zone pH, while both DCPTA and inositol were greatly contributed to the stability of the total nutrient concentration in the root zone. The DCPTA positively affected the stability of NO₃⁻ and K⁺. While the inositol had a positive effect on the stability of Mg²⁺. 4) Both DCPTA and inositol treatments were significantly improved the nutrient absorption and utilization efficiency in the plants. The DC, JC, and DC+JC treatments significantly increased the absorption and utilization efficiency of P, K, and Zn, with the increases ranging from 12.4% to 44.3%, compared with the CK. Notably, the DC+JC treatment showed the best performance in the Zn absorption and utilization efficiency, with the increase of 44.3% for them, indicating a significant synergistic effect of the combined application of DCPTA and inositol. In conclusion, the combined application of DCPTA and inositol was achieved the best to improve the tomato quality and nutrient absorption. The research findings can provide the strong reference for the year-round high-quality and efficient tomato production in multi-span greenhouses.