Soil physiochemical properties are considered as the main driving force for the changes of community and spatial distribution of soil microorganisms. Exploring the relationship between soil physiochemical properties and soil microorganisms is one of the hot topics in ecology and soil science. In this study, changes of soil physicochemical properties and the composition of soil microbial community were measured along four distances from two types of Populus euphratica's trunk (big and small mature individuals) under their crown. Four distances included two positions that far from big Populus euphratica's trunk within 3 m (DB_{0-3 m}) and ranged from 3 to 6 m (DB_{3-6 m}), the position far from small Populus euphratica's trunk within 3 m (DS_{0-3 m}), and control group (CK) that distance from both big and small Populus euphonicus's trunk at least larger than 9 m. Then, differences in microbial communities, canonical correspondence analysis and Spearman correlation analysis were used to explore relationships between soil physicochemical properties and distribution of soil microorganisms. The results showed that (1) among four sampling positions, fine root biomass, soil water content, soil organic matter, total nitrogen, total phosphorus and total salinity were the highest in DB_{0-3 m}, the middle in DB_{3-6 m}, and the lowest in DS_{0-3 m} and CK (DB_{0-3 m} ≥ DB_{3-6 m} ≥ DS_{0-3 m} ≥ CK) (P<0.05). The contents of these soil physicochemical properties in DB_{0-3 m} were 3.97, 1.13, 3.71, 3.03, 1.49 and 1.95 times of these in DS_{0-3 m}, respectively. On the contrary, soil bulk density did not show the significant difference among four sampling positions (P>0.05). (2) At the class level, spatial distributions of the top 10 bacteria and fungi in abundance were significantly different in the four sampling positions. In bacteria, Rhodothermia and γ-metamorphosis were the dominant class in DB_{0-3 m} (their relative abundances were 0.27 and 0.28, respectively), while Bacteroides were the dominant class in other positions (relative abundances were 0.37, 0.26, and 0.26 in DB_{3-6 m}, CK, and DS_{0-3 m}, respectively). In fungi, Sordariomycetes were the dominant class in DB_{0-3 m} and DS_{0-3 m} (relative abundances were 0.27 and 0.10, respectively), while Dothideomycetes were the dominant class in DB_{0-3 m} and DS_{0-3 m} (relative abundance were 0.09 and 0.16, respectively). (3) There were significant differences in bacterial and fungal community composition among four sampling positions. The fungal and bacterial communities in DB_{0-3 m} were similar to those of DB_{3-6 m}, while which were similar between DS_{0-3 m} and CK. (4) The results of typical correspondence analysis and Spearman analysis showed that the community composition of soil microorganisms was mainly affected by soil salinity, fine root biomass, soil water content, soil organic matter, total nitrogen and total phosphorus. Compared with other factors, soil salinity had the greatest contribution to the change of community composition of soil microorganisms. To sum up, the composition and spatial distribution of soil microbial community vary along distances from Populus euphratica's trunk, which is the result of the joint actions of material exchange and nutrient flow between plant root and soil, and habitat selection of soil microorganism. To some degree, the changes of composition and distribution of soil microbial community negatively affect the germination and growth of seedlings. As a result, this negative effect makes less plant growth under the crown of Populus euphratica.