Abstract: A complex vertical-flow wetland consisting of an upstream flow cell and a downstream flow cell was constructed in an experiment for exploration of effects of addition of earthworms and loaches into the two cells on organic carbon and nitrogen in form and content in the plant root zone of the constructed wetland. Results show that the addition of loaches increased the average content of total organic carbon (TOC), easily oxidized organic carbon (EOOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC) and nitrate nitrogen by 16.7%, 10.8%, 19.1%, 33.8% and 68.4%, respectively, and decreased the average content of ammonia nitrogen by 14%, while the addition of earthworms increased the content of TOC, EOOC, MBC, DOC and nitrate nitrogen by 74.6%, 39.7%, 40.4%, 45.1% and 91.8%, respectively, and decreased the content of ammonia nitrogen by 42.8%. Obviously the effects of the addition of earthworms were higher than those of loaches on organic matter, nitrate nitrogen and ammonia nitrogen. Correlation analysis shows that the content of TOC, EOOC and MBC was significantly related to the content of nitrate nitrogen (P<0.01). All the findings indicate that introduction of animals into wetlands increases organic carbon content in the plant root zone of the constructed wetland, and stimulates nitrification process in the wetland, thus increased the content of nitrate nitrogen in the soil.