In this study, an innovative integrated two-stage (ITS) anaerobic bioreactor was designed and constructed in pilot scale. The integrated reactor used the dual-cylinder configuration to separate the acidogenic stage in inner cylinder with the methanogenic stage in outer cylinder. The reactor was operated for 184days treating food waste with elevated organic loading rates (OLR). The ITS reactor showed high efficiency and stability. In the stable operation phases, the organic load was 3.0kgVS/(m³·d), volumetric gas production rate reached an average of 1.69m³/(m³·d), and highest value is up to 2.72m³/(m³·d); the gas production rate was 0.57m³/(kgVS·d), and the organic solids removal rate was 77.2%. Due to phase separation effect, pH value of outer cylinder was about 0.3~0.4unit higher than that of inner cylinder, the average volatile fatty acids (VFAs) and soluble chemical oxygen demand (sCOD) concentration of outer cylinder was 25% and 23% lower than that of inner cylinder, respectively. The integrated two-stage (ITS) anaerobic reactor realized the separation of acidogenic and methanogenic phases in one reactor. The inner acidogenic phase performed the hydrolysis and acidogenic steps and reduces the impact of acid accumulation on the outer methanogenic phase, which played a key role in the stable operation of the reactor.