Abstract: To analyse the optimal condition of photocatalytic removal of indoor air contaminant by air cleaner, an experimental system of photocatalytic degradation of HCHO was constructed and two photocatalytic TiO2 films were coated by dipping method on the granular active carbon and the netlike active carbon,respectively. The results showed that the photocatalytic removal of HCHO was controlled by mass transfer process and pho- tocatalytic reaction process in the higher HCHO concentration,and the photocatalytic reaction switched from mass transfer process to photocatalytic reaction process with the increasing of flow velocity,and the removal of HCHO by TiO₂ film coated on netlike active carbon was higher than that coated on granular active carbon. However,in the lower HCHO concentration,the removal of HCHO was reduced with the increasing of flow rate for the residence time of HCHO on the surface of TiO₂.Those experimental results were useful to the ap- plication of photocatalytic technology.