Abstract: Traditional fertilization for greenhouse vegetables relies on experience. In order to ensure precise fertilization, this study investigated the relationship between leaf dry matter content and leaf phosphorus concentration in tomatoes, cultivated under different phosphorus supply levels through field experiments. After establishing the dilution curve model using leaf dry matter and phosphorus concentration data, a diagnostic analysis of the phosphorus nutritional status was constructed, and recommended fertilization amount for tomatoes was suggested. This study provided both theoretical and practical guidance for phosphorus nutrition diagnosis and phosphorus supply optimization in substrate-cultivated tomato. In this study, the Jinpeng ‘101’ tomato variety was used as plant material and five phosphorus supply levels (0%, 40%, 80%, 100%, and 140%) were designed based on standard Yamasaki tomato nutrient solution formula. These treatments represented varying phosphorus supply levels and their effects on tomato growth. The effect of phosphorus supply on leaf dry matter content, leaf phosphorus concentration, phosphorus absorption, and single fruit weight, yield, and fruit quality were analyzed. Based on experimental data, dilution curve models of the critical phosphorus concentration, critical phosphorus absorption, and phosphorus nutrition index (PNI) were established for greenhouse tomato. The analytic hierarchy process and entropy weight method was used to determine the subjective and objective weights, then, combined with technique for order preference by technique for order preference by similarity to ideal solution (Topsis) to entropy the comprehensive evaluation on of tomato growth indicators. These weights were integrated using game theory to obtain the combined weights for various growth indicators. The comprehensive evaluation scores were non-linearly fitted with the PNI to validate the accuracy and applicability of the PNI model. The results showed that the leaf dry matter content of tomatoes significantly increased with higher phosphorus supply levels, indicating that appropriate phosphorus supply promotes tomato growth. Furthermore, leaf phosphorus concentration gradually decreased as the growth stage progressed, but at higher phosphorus supply levels, leaf phosphorus concentration showed an increasing trend, confirming the essential role of phosphorus in tomato growth. Phosphorus absorption by tomato leaves also increased with higher phosphorus supply levels, indicating a close relationship between phosphorus absorption and fertilization. In terms of model construction, the tomato critical phosphorus concentration dilution curve model demonstrated high accuracy, with a root mean square error (RMSE) of less than 0.0503 and a normalized RMSE (n-RMSE) of less than 10.499%, showing strong stability and high predictive precision, making it a reliable theoretical basis for phosphorus nutrition management in tomato. Phosphorus nutritional diagnosis based on the PNI model showed that the 0% and 40% phosphorus supply treatments exhibited significant phosphorus deficiency, with PNI values is below 1, which indicated that tomato growth was limited by phosphorus. PIN values of the 80% and 100% phosphorus supply treatments closed to 1, indicating phosphorus nutritional status is sufficient, with no significant growth limitations. The 140% phosphorus supply treatment (excess phosphorus) had PNI values greater than 1, suggesting that excessive phosphorus supply may negatively affect tomato growth. Through comprehensive evaluation and nonlinear fitting of PNI, the 100% phosphorus supply was the most effective. In the Guanzhong area of Shaanxi Province, the recommended phosphorus supply for spring and autumn greenhouse substrate-cultivated tomatoes was as follows: for the seedling, flowering and fruit-setting, and maturity stages, phosphorus supply levels were 9.369, 25.292, and 18.743 kg/hm² (spring) and 9.680, 12.240, and 5.997 kg/hm² (autumn), respectively. These phosphorus supply levels align with various growth indicators of tomatoes and provide scientific support for optimizing phosphorus management in tomato production.