The study with gnotobiotic microcosm showed within the range of test soil moisture contents, the feeding activity of Caenorhabditis elegans on Bacillus subtilis promoted the latter' s proliferation, and enhanced soil respiration significantly. The increment of B. subtilis number varied with soil moisture content, and decreased in the order of 23% > 17% > 28% . The interaction of C. elegans and B. subtilis increased the contents of soil mineral N and NH4 + -N significantly, indicating that soil nitrogen mineralization was markedly promoted. A higher nitrogen mineralization rate was observed under 23% soil moisture content.