Background and aims <p>The degradation of desert steppe in arid and windy areas is associated with biodiversity loss, reduced soil quality, and diminished ecosystem functions. However, the mechanisms by which this affects ecosystem multifunctionality (EMF) remain unclear, particularly the interactions between biotic and abiotic factors and their relative contributions.</p> Methods <p>This study employed a spatiotemporal substitution method, evaluating desert steppe with varying levels of degradation as experimental sites. By integrating a random forest model with structural equation model (SEM), we quantitatively analyzed the factors influencing EMF and their relative contributions, thereby elucidating the EMF maintenance mechanisms during desert steppe degradation.</p> Results <p>Desert steppe degradation significantly reduced EMF. However, different functional indicators responded differently to desert steppe degradation. Grassland degradation was manifested as significant declines in both plant and microbial diversity, coupled with a concomitant reduction in soil fertility, increased soil pH and bulk density, and decreased soil clay content. EMF showed a significant positive correlation with plant and microbial diversity, but a significant negative correlation with soil pH and bulk density. Moreover, grassland degradation was accompanied by a loss of soil clay content and increased sand content, which indirectly impacted plant and microbial diversity, causing decreased EMF.</p> Conclusions <p>Desert steppe degradation reduces the multifunctionality index; abiotic pathways indirectly reduce EMF, and biodiversity is an important driver of EMF change. In the early stages of grassland degradation, biodiversity dominates ecosystem functions; as degradation intensifies, soil physical and chemical properties deteriorate, and abiotic factors become the main limiting factors.</p>