The performance and the characteristics of a laboratory scale up-flow multistage anaerobic reactor (UMAR) were investigated using cassava starch wastewater. The experimental results showed that the formation of anaerobic granules in UMAR system was facilitated and short period to start up. Usually, in 40 d after starting up, COD removal efficiency was kept above 84% and VSS/TSS increased from 78% to 90.4%. The UMAR reactor was high effective. Its COD removal keeps about 75% when HRT is 4 h, inflow COD concentration is 6 250 mg/L and volumetric loading is 24 kg/(m3 x d). And UMAR reactor has excellent resistance to the impact of high load, low pH and variation of water quality.