Rapid human populations growth in inland arid regions of northwestern China has resulted in rapid oasis expansion, mainly through transforming natural grasslands to arable land, afforested forest and shrub plantations. However, little is known about how different oasis expansion regimes affect soil biodiversity and ecosystem function. In this study, we measured the abundance of nine dominant functional groups of soil biota across multiple trophic levels, including soil macrofauna (oligochaetes, ants, predatory arthropods and herbivorous insects), soil mesofauna decomposers (Oribatida and Collembola) and soil microbial decomposers (bacteria and fungi) in natural grasslands (NG), arable lands (AL), tree (Populus gansuensis) plantations (TP) and shrub (Haloxylon ammodendron) plantations (SP). The study was performed in Zhangye Oasis in the middle reaches of the Heihe River Basin in northwestern China. We measured the contents of soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP), as well as the activities of four soil enzymes (catalase, urease, sucrase and phosphatase). The results showed the following important findings. First, the land conversion of NG to SP significantly lowered the abundance of Oribatida and herbivorous insects, while increasing the abundance of Collembola, predatory mites and fungal OTU numbers. However, converting NG to TP significantly increased the abundance of predatory arthropods, herbivorous insects, Collembola, Oribatida, predatory mites and numbers of both bacterial OTUs and fungal OTUs, whereas converting NG to AL significantly increased the abundance of all the above plus oligochaetes. Second, converting NG to either TP or SP significantly enhanced SOC and TN stocks, whereas converting NG to AL significantly enhanced the above plus TP stocks. Finally, converting NG to either SP, TP or AL significantly enhanced the activities of catalase, urease, sucrase and phosphatase, but these four soil enzymes show significantly higher activity in AL and TP sites with irrigation than in SP sites without irrigation. Our results suggest that different oasis expansion regimes significantly and differentially affect the structure and diversity of the desert soil food web, which in turn, cascades down to ecosystem functioning. Understanding the responses of both different soil food web components and of different ecological function variables to changes in land use and management level is essential for developing novel and more effective strategies for oasis ecosystem management in arid regions worldwide. Overall, this study provided key insights into the assessment of the functional stability of the oasis ecosystem.