An Internal Circulation Impinging Stream Biofilm Reactor (ICISBR) was developed and used for treatment synthetic organic wastewater with corncob as biofilm carriers. Effects of COD loading rates and aeration rates on COD removal and DO contents were investigated. COD removal efficiency increased together with effluent COD with increasing COD loading rates. As the aeration rate was increased, the DO content also increased together with COD removal efficiency up to an optimum aeration rate of 0.3m3h-1. Beyond this optimum aeration rate a significant decrease in DO content and COD removal efficiency were experienced. This study could provide theoretic basis for the ICISBR treating organic wastewater.