Organic amendments are considered to be able to revitalize saline-alkali soils; nonetheless, whether the moss powder as a novel amendment increases the organic and inorganic carbon of saline-alkali soils remains unknown. This study evaluated the effect of the moss powder amendment at different rates (0, 2.5, 5, 10, 15, and 20% w/w). Other than the conventional statistics (linear regression models and ANOVA), the interpretable artificial intelligence (XGBoost models and SHAP technique) was also innovatively used to identify the critical drivers and thresholds of soil carbon dynamics. The conventional statistics showed that the peak values of the concentration (and density) of soil organic, inorganic, and total carbon occurred at the 20 (10), 0 (2.5), and 20% (10%) rates, respectively. However, the interpretable artificial intelligence model consistently identified 10% as the optimal rate of moss powder amendment. At this rate, the saline-alkali soil health was improved, that is, reducing soil salt concentration, pH, and electrical conductivity without compromising soil bulk density, porosity, and water content, as well as increasing soil available nutrients, soil organic carbon density, and total carbon density without significantly negatively impacting soil inorganic carbon density. This study highlighted the use potential of moss powder amendment and the undeniable prospects of interpretable artificial intelligence in improving saline-alkali soil health.