【Objective】Coastal saline-alkali soil is plagued by prominent issues such as high salinity, poor structure, and nutrient imbalance, which severely restrict regional ecological security. The application of bio-based amendments is an effective measure for ameliorating saline-alkali soil; however, its effect on the quality of coastal saline-alkali soil remains unclear. 【Method】Using Olea europaea L. and Taxodium mucronatum Ten. as test tree species, and coastal saline-alkali soil in the reclamation area of Taizhou City as the research object, two bio-based amendments, Amendment 1 (Camellia oleifera husk + humic acid, 1:1, m:m) and Amendment 2 (biochar + humic acid, 1:1, m:m), were applied at five treatment levels: CK (no amendment), T1 (Amendment 1, 2.5 kg·plant-1), T2 (Amendment 1, 5.0 kg·plant-1), T3 (Amendment 2, 2.5 kg·plant-1), and T4 (Amendment 2, 5.0 kg·plant-1), to evaluate their effects on soil quality. A three-year field experiment was conducted to systematically determine the indicators of soil physical structure, chemical properties, and enzyme activities. Principal component analysis (PCA) was employed to construct soil quality indices based on the total data set (TDS) and the minimum data set (MDS), respectively, for comprehensively evaluating the improvement effects of different amendment schemes. 【Result】Soil quality was comprehensively evaluated by establishing both TDS and MDS based on PCA. The results showed that: (1) Both bio-based amendments demonstrated certain ameliorative effects on the saline-alkali soil. Among them, the 2.5 kg·plant-1 biochar treatment showed the most comprehensive improvement in coastal saline-alkali soil, significantly enhancing soil aggregate stability, increasing the contents of soil organic carbon, total nitrogen, and total phosphorus. This treatment also promoted the accumulation of calcium and magnesium ions while reducing the relative proportion of sodium ions, and effectively boosting the activities of soil urease and polyphenol oxidase. (2) The PCA results indicated that bulk density, mean weight diameter, soil organic carbon, total phosphorus, nitrogen-phosphorus ratio, and urease could serve as MDS for soil quality evaluation in the 0-20 cm soil layer of coastal saline-alkali soil, while the MDS for the 20-40 cm soil layer included bulk density, R0.25, organic carbon, cation exchange capacity, carbon-phosphorus ratio, Ca, and Na/Mg. (3) The evaluation results of soil quality index (SQI) showed that the SQI of the T3 treatment was higher than that of other treatments. (4) Regression analysis results revealed that the SQI constructed based on TDS and MDS in both 0-20 cm and 20-40 cm soil layers showed an extremely significant positive correlation (P < 0.001), verifying that the MDS could be used as an evaluation indicator to characterize the improvement effect of coastal saline-alkali soil. 【Conclusion】The combined biochar treatment (2.5 kg·plant-1) exhibits the greatest and most comprehensive improvement in coastal saline-alkali soil, achieving a significant enhancement of soil quality with considerable potential for popularization and application. In addition, the layered minimum data set established in this study can provide data support for the monitoring and evaluation of soil quality in this region.