Abstract: In this work,at a pressure of 2.0 MPa and room temperature,the effects of gas and liquid flowrates, liquid viscosity and operation pressure on the dynamic liquid holdup were investigated in a downward flow and upward flow fixed-bed reactor. With an air-water-solid packing system, experimental results show that the dynamic liquid holdup increased with an increases of liquid mass flowrates.It decreased with an increasing of gas volume flowrates and porosity of packed bed. It was also shown that there was no large effect on dynamic liquid holdup with an increase of liquid dynamic viscosity. The correlations of dynamic liquid holdup was also given under these two kinds of operation.