Abstract: Haloxylon ammodendron was introduced to the Minqin region from Xinjiang province in the 1960s. It became the primary species for windbreak and sand stabilization planting. The area in H. ammodendron plantation forest in Minqin County is about 3.5×10⁴ ha, 51.5% of the total plantation forest area. Degradation H. ammodendron forest had been observed since the 1970s, seriously threatening the survival and development of the Minqin Oasis. The aim of this study was to investigate the physicochemical and biological properties of soil under H. ammodendron forests with different degradation states in the Minqin oasis-desert ecotone, Gansu. 12 plots were selected in the degradation gradient; soil samples were collected from 0-5 cm, 5-10 cm, 10-20 cm depths from a representative area in each plot. Each plot was assigned (using vegetation indices) to one of four degradation grades (no degradation, light degradation, moderate degradation and severe degradation) using hierarchical cluster analysis. The soil physicochemical properties, microbial number, and enzyme activities were analysed. The effect of degradation of H. ammodendron forest on soil bulk density, total salt content, cation exchange capacity was not obvious, but soil organic gradually decreased and pH changed complexly with increasing degradation and increasing of soil depth. The total number of microbes and microbe species decreased with increasing soil depth; numbers of bacteria were much higher than actinomycetes in 0-5 cm soil depth, but they were similar in deeper soil layers. Fungi were not prevalent in any soil layers.Increased degradation was not associated with changes in the number of fungi observed.Enzyme activity decreased with increasing soil depth with increased degradation. The impact of degradation of H. ammodendron forest on protease activity, catalase activity, urease activity was greater than for invertase activity, the former showed greater sensitivity to changes in resources and environment. There were strong correlations among soil physicochemical properties, number of soil microbes and soil enzyme activities, but the correlation among soil physicochemical indicators, between soil bulk density, number of actinomycetes and other indicators were not significant. Soil fertility and biological properties in degraded H. ammodendron plantations have declined; restoration of the soil is necessary for restoration of these forests.