Yellow soil in Bijie of Guizhou was taken as the research object, and simulation test in the greenhouse was carried out to study the effect of foam sand on pore structure by incorporating equal amount of foam sands with different diameters, which include 0.5-2 mm (1T treatment), 2-7 mm (2T treatment) and 7-10 mm (3T treatment). The results showed that soil aeration porosity increased with the increase of diameter of the foam sand under the same ratio of addition, compared with CK (without foam sand), 1T, 2T and 3T treatments increased soil aeration porosity by 4.68%, 7.39% and 14.5%, respectively. Foam sands with different diameters had different effects on pores with different equivalent diameters, 1T, 2T, and 3T treatments increased porosities with 200-500 μm, 1 000-2 000 μm and >2 000 μm in diameters, respectively. Foam sands improved pore connectivity compared with CK, but no significant difference was found among 1T, 2T and 3T treatments. 2T and 3T treatments improved soil bulk density and total porosity most, and 2T treatment improved the proportion of soil aeration porosity the second most. Therefore, from the perspectives of aeration pores, soil porosity proportions and pore morphology, foam sand with 2-7 mm diameter is best in improving clayey yellow soil.