Abstract: Numerical simulations of different slurry bed hydrocracking reactors were carried out using Euler-Euler multiphase model and RNG k-ε turbulence model. In the simulations, bubble column reactor and airlift loop reactors with different diameter of draft tube were chosen to investigate the similarities and differences in gas holdup and axial liquid velocity. The results demonstrate that liquid circulation flow is formed in all three kinds of reactors. The draft tube divides the whole flow field into riser and downcomer, located in and out of the tube, respectively and at the same time, can increase the liquid velocity both in riser and downcomer, rising gas holdup both in the downcomer and the entire reactor. A conclusion can be drawn that airlift loop reactor is better than bubble column reactor for slurry bed hydrocracking process.