Abstract: Dissolved organic matter (DOM) in wetland soil is a sensitive indicator reflecting the change of soil organic carbon pool, and its variation characteristics and driving factors have been a research hotspot at home and abroad. However, there is little research on whether it has regional differences. In this study, we selected marsh wetlands in four typical climatic regions of Da Hinggan Mountains, Inner Mongolia, Qinghai, and Xizang, and used ultraviolet-visible spectroscopy (UV-Vis) and three-dimensional fluorescence excitation-emission matrix (3D-EEM) techniques to investigate the effects of climate change on the wetland ecosystem, combined with PARAFAC analysis, the spatial variation of soil DOM and its environmental driving mechanism were systematically explored. The results showed that the content and spectral characteristics of soil DOM were significantly different in different regions. The content of soil DOM was the highest in Da Hinggan Mountains, and the aromatization and humification of soil DOM were higher in Qinghai affected by high altitude and extreme climate, the soil DOM of the marsh wetland on the Qinghai-xizang plateau was dominated by abiotic characteristics, and the abiotic index (BIX) value was the highest. In addition, the spatial distribution of DOM was significantly correlated with latitude and longitude, showing a zonal pattern. With the increase of latitude, the content of DOM increased and the degree of humification decreased, reflecting the cooperative regulation of the climate-vegetation-microorganism system. Soil pH was negatively correlated with DOM content, but positively correlated with aromatic components. Structural equation modeling showed that geospatial location was the main controlling factor for DOM differentiation at large regional scales, and that soil pH could be used as a proxy for DOM variability at large regional scales, and vegetation biomass played a dominant role at the local scale.