Abstract: The numerical simulation of slurry bed hydrocracking loop reactor was carried out. The standard k-ε turbulence model and the Euler multiphase flow model were used for the simulation of gas-liquid two phase turbulence flow. The effect of difference in physical properties of fluid, like liquid density, gas density and liquid viscosity on gas holdup and flow field was tested and compared. The results show that the gas density has little effect but the liquid viscosity has a significant effect on flow field and gas holdup. The liquid density affects the gas holdup, but it has a little effect on the flow field.