Abstract: Herbicide application has attracted increasing global attention as it severely affects the structure and function of ecosystems. In China, the effects of herbicide on soil fauna community structure and diversity have gained considerable attention in recent years. As a form of herbicide, acetochlor could accumulate in some soil ecosystems, thus the wide use of acetochlor could have serious effects on soil ecosystems. Unfortunately, the effects of acetochlor on the structure, biodiversity and vertical distribution of soil biotic communities have remained largely unclear. Acetochlor was applied with three concentrations (10.80 mL·L^-1 of high concentration, 3.20 mL·L^-1 of middle concentration and 0.54 mL·L^-1 of low concentration) and a control (distilled water) in maize field in May, July and September of 2012 in Hulan District of Harbin City, China. And 7 days after acetochlor application every time, soil samples were collected to investigate the composition, biodiversity and vertical distribution of soil meso/micro-fauna. In the study, 15 groups and 4 648 individuals of soil meso-fauna and micro-fauna were captured. The fauna belonged to 2 phyla, 4 classes and 10 orders. Oribiatida and Mesostigmata were dominant groups (69.12%), Onychiuridae, Isotomidae, Paronellidae, Sminthuridae, Prostigmata, Coleoptera and Hymenoptera were common groups (27.59%), and the others were rare groups. The results showed that different concentrations of acetochlor had significant effects on soil fauna community. In terms of the Sorenson and Morisita-Hron indices of soil fauna community, the difference between high and medium concentrations was largest. Also the difference between high concentration treatment and the control was lowest. Then a moderate difference was noted between high and low concentrations. The above results suggested that differences among soil fauna community structures increased with increasing acetochlor concentration. Except for dominance index, all the other diversity indices of CK were significant different at P < 0.05 from those of medium and low concentrations; and signifcant different at P < 0.001 from those of high concentration. The density of soil fauna in 0 5 cm soil layer under different acetochlor concentrations were in the order of CK > low concentration > medium concentration > high concentration in May, July and September. However, the relationships between soil fauna density and acetochlor concentrations in the deeper soil layers were insignificant. The changes in soil fauna diversity became significant with increasing acetochlor concentration. This was largely attributed to fluctuations in soil fauna counts and groups in the 0 5 cm soil layer. The results suggested that the use of high concentration acetochlor not only disturbed soil ecosystem, but was also harmful to soil environmental health. It was critical to have the appropriate concentration of acetochlor in order to limit any harmful effects on soil environmental conditions and soil fauna communities in farmlands.