The compartmentalized anaerobic reactor (CAR) is a novel, promising high-rate bioreactor (R) for anaerobic digestion process. The feasibility of early-warning on the performance of lab-scale CAR was investigated. CAR showed less stable performance at high organic loading rates (OLRs) than that at regular OLRs. At high OLRs, the system in response to the fluctuation of influent chemical oxygen demand (COD) concentration showed higher variation in terms of effluent COD and volatile fatty acids (VFA) concentration. Two newly defined parameters, VLR saturation (S-VLR) and VFA saturation (S-VFA) could be used as indicators for early-warning on the performance of anaerobic reactors. The system performance was relatively stable when CAR was operated at regular OLR, during which S-VLR and S-VFA were below 0.89 and 0.4 respectively. It tended to be unstable under high OLR conditions when S-VLR and S-VFA were close to 1, and deteriorated when S-VLR and S-VFA were above 1. (C) 2015 Elsevier B.V. All rights reserved.