Abstract: Based on the reaction data of catalytic diesel liquid-phase hydrogenation in a tubular reactor with ratio of height to diameter of 17 and a power-law type HDS apparent kinetic model, the impact of fluid flow and mixing on the reaction with and without a mixer of ceramic membrane was investigated. The results without the mixer show that the liquid flow inside the tube deviates from plug flow model. Adding the mixer makes the liquid flow inside the tube approach plug flow model and the average relative deviation is only 2.72% which explains the main cause of deviation is mixture of gas and liquid rather than back-mixing. Fluid flow inside the liquid hydrogenation tube can be regarded as an ideal plug flow due to the deviation of axial difusion model is close to that of plug flow model.