Tree planting is widely recognized as an effective strategy for enhancing terrestrial carbon sequestration, playing a crucial role in mitigating global climate change. However, our understanding of how it may affect soil fauna communities remains scarce. Here, we performed a global meta-analysis with 14 281 paired observations to evaluate tree planting effects on soil fauna abundance, biomass, and diversity across multiple former ecosystem types. Results showed that (i) tree planting had limited overall effects on soil fauna communities, only increasing Acari abundance, Protozoa abundance and Arthropod biomass by 36.9%, 56.9% and 777.3%, respectively, and decreasing the taxonomic richness of Collembola, the Pielou index of earthworm, and the Simpson index of Protozoa by 17.9%, 38.7%, and 77.1%, respectively; (ii) afforestation in non-forest lands showed strong positive effects on soil fauna abundance and diversity, especially in deserts where the abundance and Shannon-Wiener index of total soil fauna were increased by 92.5% and 65.8%, respectively, while reforestation in former forest lands generally had negative impacts; and (iii) tree planting effects on soil fauna were mediated by stand characteristics (e.g. stand age, canopy density, tree diameter) and pre-planting soil properties (e.g. bulk density, pH, carbon, nitrogen), but not by tree species type (leaf type or mycorrhizal association). These results demonstrate the contrasting effects of tree planting on soil fauna communities among different former ecosystem types, highlighting the importance of considering the legacy of former ecosystems when designing tree planting policies to restore/enhance carbon sequestration and biodiversity conservation under global environmental change scenarios.