The start-up characteristics of internal circulation anaerobic reactor were studied using anaerobic sludge of UASB as vicinal sludge. The concentration of influent COD was kept at 2500mg/L initially, then the influent flow increased from 1L/h to 2.5L/h gradually, and the removal rate retained around 85.0% to 93.5%. During the middle-period of the experiment, the influent flow was maintained at 2.5L/h, and the influent COD concentration was gradually increased from 2500mg/L to 10500mg/L, the removal rate of 91.2%~94.6% was obtained now. At the end period of the experiment, the influent COD concentration was kept at 10500mg/L, and the influent flow was increased from 2.5L/h to 3L/h gradually. When the volume loading was improved to 55.04kg COD/ (m3 • d), the COD removal rate reached 88.3%.