Abstract: In this paper, varying the pressure from the atmospheric pressure to 2.0 MPa, the effects of liquid and gas mass flowrates, liquid viscosity, packed particle size, packed height and pressure on the dynamic liquid holdup were investigated in a down flow trickle bed reactor. The experimental result show that the dynamic liquid holdup increases with the liquid mass flowrates and decreases with the gas mass flowrates, packed height and porosity of packed bed. The experiments also show that there are no large effects on the dynamic liquid holdup with increasing liquid viscosity.