Photocatalytic degradation process has been recognized as a low-cost, environmental friendly and sustainable technology for water and wastewater treatment. As a key carrier of the photocatalytic process, the semi-conduct photoreactor has been employed in many studies. Analysis and modelling of hydrodynamics and degradation kinetics in the three phase system can provide useful information for process design, operation and optimization. We have modelled the hydrodynamics and degradation kinetics in an annular photocatalytic bubble column reactor using an Eulerian multi-fluid approach. All the results (gas holdup, fluid flow patterns and organic concentrations) were evaluated against experimental data from our lab or literature reports. The local information on gas holdup, solid particle concentration, light intensity as well as organic pollutant concentration has been obtained. The simulation results reveal that the degradation rate of organic pollutants is controlled by the local hydrodynamics and light intensity. By combining CFD and degradation kinetics models, the mechanisms of governing the photocatalytic reaction can be determined. The computational models will also help optimize reactor design to improve the hydrodynamics and light intensity distribution and provide guided information for scale-up. (C) 2011 Elsevier B.V. All rights reserved.