[Objective] The particle size distribution and fractal characteristics of soil under low-efficiency poplar forests in Ordos region were studied to provide a basis for the cause analysis and transformation of low-efficiency poplar forests in this region, and to provide a reference and decision-making support for the scientific management of poplar plantations.[Methods] We used a Mastersizer 3000 laser diffraction particle size analyzer to measure soil particle size, and a fractal dimension model of soil particle volume to calculate the fractal dimension D, and measured soil nutrients.[Results] ① The main components of soil particles in the low-efficiency poplar forests were fine sand (42.33%), ultra-fine sand (15.72%), and medium sand (19.77%). The main soil texture type was sand and the fractal dimension D of the soil particles was in the range of 1.222 5~2.204 5, which was at a low level. ② The fractal dimension D of soil particles was positively correlated with the silt, ultra-fine sand, and fine sand content, but was negatively correlated with the medium sand, coarse sand, and ultra-coarse sand content. ③ With an increase of the soil layer, the soil particle content with particle size <250 microns increased, whereas the soil particle content with particle size >250 microns decreased. The fractal dimension D value of soil particles increased with an increase of the soil layer; however, the increase was not significant. ④ The relationship among the fractal dimension D of soil particles and the soil organic matter, total nitrogen, available nitrogen, and available phosphorus content was not significant, and the change of soil nutrient content had no significant effect on fractal dimension D.[Conclusion] Sand is the main component of soil particles in low-efficiency poplar forests in the Ordos area. The fractal dimension of the soil is low and the soil structure is very uneven. This type of soil structure is very harmful to the normal growth and development of poplar. This poor soil structure leads to the formation of low-efficiency poplar forests to a certain extent. The soil structure under the forest could be improved by prevention and transformation.