Ecosystem dynamics are driven by the complex interplay of multiple interacting factors. Understanding how ecosystem services (ES) change over time and space, along with their trade-offs and interactions, is key to promoting sustainable development. This study identified four key ESs in the arid zone of northwest China: habitat quality (HQ), soil conservation (SC), water conservation (WC), and net ecosystem productivity (NEP). To better analyze the nonlinear relationships between ES trade-offs/synergies and their drivers, this study innovatively integrates Pearson's correlation analysis, generalized additive models, Bayesian belief networks, and geographically convergent cross mapping models in a multimethod fusion framework to analyze mechanisms of action. The key results of the analysis are presented as follows: (1) The spatial distribution of the four ESs is similar and exhibits a roughly high-north and low-south distribution pattern. (2) From 2000 to 2022, SC exhibited an upward trend, while WC generally showed a declining trend, primarily with a slight decrease. NEP and HQ remained relatively stable throughout the study period. (3) ES trade-offs and synergies exhibit significant spatiotemporal heterogeneity, with synergistic relationships dominating. Specifically, the synergy between HQ and SC is the strongest, whereas the trade-off between NEP and HQ is the most pronounced. (4) Trade-offs and synergies primarily exhibit unidirectional causality with natural factors, while human activity factors show weak bidirectional causality. This study holds important theoretical and practical significance for promoting ecological environmental protection and coordinated economic development in the arid regions of northwest China.