Abstract: In May, July and September 2012, four treatment plots with different concentrations of effective microorganisms (EM) compost were established (control, low, medium, and high concentration) in a typical black soil farmland in Harbin. We investigated the effects of different EM compost concentrations on the composition, vertical structure, seasonal dynamics, and diversity of micro- and medium-sized soil faunal communities. A total of 7860 individuals (with the average density of 49125 ind·m^-2) were captured which were classified into 30 groups, belonging to ten classes and three orders. Overall, the number of group and density of fauna increased with the increasing concentration of EM compost. However, the density was lower in the low concentration plot than in the control. The vertical distribution of faunal communities was characterized by surface clustering and there was a strong seasonal variation. The diversity indices of faunal communities increased with increasing the EM compost concentration, and the soil organic matter had a relatively greater contribution to such diversity changes. The response of groups to EM treatment was species-dependent. Frequent and dominant groups had strong adaptability to changes in the soil environment, while the rare groups were more sensitive. This study revealed that EM compost could promote the community structure and increase the diversity of the faunal community in the black soil farmland.