Analysis of benthic micro-invertebrate community structure from the Pyeonghwaui Dam was investigated from May 2006 to October 2008. Total taxa of benthic micro-invertebrates were 5 phylum, 8 class, 15 order, 44 family, and 97 species in 2006, and 5 phylum, 7 class, 15 order, 48 family, 103 species in 2008. Mean dominance index at St. 1 to St. 5 were 0.36, 038, 0.38, 0.21 and 0.29. Mean species diversity at St. 1 to St. 5 were 3.84, 3.34, 3.13, 4.84 and 4.28. Although the dominance index of Lentic area was higher than Lotic, but the diversity was lower than Lotic area.