[Objective] The soil and water conservation effect mechanism of the two core elements (slope and vegetation) in a slope-to-terrace project were systematically analyzed to provide specific methods for multi-index mechanism research, to supplement and improve the ecological effect theory of water conservation projects, and to provide theoretical guidance for the practice of ecological civilization construction. [Methods] Slope and vegetation factors were comprehensively considered, and a variety of mathematical models were used to deeply analyze their water conservation effect mechanisms. [Results] ① Based on a linear model, the linear component decomposition of the total soil and water conservation effect of the five indicators in the full text under the same spatiotemporal conditions was realized. Furthermore, based on the precise calculation of the relative contribution rate of each component, the real source of the soil and water conservation effect of the slope-to-terrace project was revealed for the first time in a theoretical sense. ② Based on multiple regression analysis, the optimal mathematical model was selected from a large number of alternative models, and the specific influencing factors and mechanism of the soil and water conservation effect of the above components were profoundly revealed. ③ Based on structural equation modeling (SEM), the rationality of the specific theoretical model including two latent variables (physical factor and chemical factor) reflecting the soil and water conservation effect of the five indicators in the full text was verified. By SEM group analysis, the preset models under the two slope conditions were fitted at the same time, clearly and intuitively showing the internal relationship between the factors and the differences in the mechanisms of the soil and water conservation effect under different slope conditions. ④ Based on principle component analysis, a comprehensive factor containing 80.8% of the information of five original variables was constructed, and the evaluation index was changed from five dimensions to one dimension, so as to realize the overall comprehensive quantitative evaluation of soil and water conservation effects. [Conclusion] Based on advanced data analysis methods, deep integration of research conclusions on the mechanism of the multi-factor soil and water conservation effect can be achieved, which deepens people’s understanding of its specific mechanism. It can also provide a methodological reference for the research of multi-index mechanisms, help to build professional mathematical models with higher predictive accuracy, and improve the efficiency of soil and water conservation practice.