The performance of a novel anaerobic bioreactor, spiral automatic circulation (SPAC) reactor, was investigated in lab-scale. The results showed that the average COD removal efficiency was 93.6% (91.1%-95.7%), with influent concentration increased from 8000 mg/L to 20 000 mg/L, at 30 degrees C and hydraulic retention time (HRT) of 12 h. The removal efficiency remained at 96.0%-78.7% when HRT was shortened from 5.95 h to 1.57 h, as the influent concentration was kept constantly at 20 000 mg/L. The highest organic loading rate (OLR), volumetric COD removal rate and volumetric biogas production of the SPAC reactor were 306 gCOD/(L x d), 240 g/(L x d) and 131 L/(L x d), respectively. When increasing influent COD concentration (from 8000 mg/L to 20 000 mg/L), the effluent COD concentration maintained at low level (852 mg/L for average) with volumetric COD removal rate increased by 162% and volumetric biogas production increased by 119%. With reduced HRT (from 5.95 h to 1.57 h), the volumetric COD removal rate and volumetric biogas production were increased by 191% and 195%, respectively. The SPAC reactor shows good performances in adapting the continuous change of influent COD and HRT.