The bitumen cracking reaction under sub- and supercritical water environments in H-2 or N-2 atmosphere using activated carbon (AC) supported nickel catalyst was studied. The sub- or supercritical water provided a unique homogeneous, acidic reaction system for the bitumen cracking reaction, which obviously promoted the bitumen conversion and selectivity of the middle distillates (kerosene and gasoline), and restrained the formation of carbon deposition, if compared with the conventional pyrolysis reaction without water addition. Moreover, the active in-situ H-2 source was provided by the water gas shift reaction in the sub- and supercritical water environment, thereby enhancing the catalytic activity of bitumen cracking. (C) 2016 Elsevier B.V. All rights reserved.