Abstract: With [Ti(OBu)₄] as raw materials,nanometer TiO₂was prepared by using sol-gel process,then the sol was applied to ACF(Activated Carbon Fiber) filter material by soaking method.The static and dynamic comparative study of the original sample and treated sample of ACF filter material were carried out with respect to the photocatalysis and oxidation of formaldehyde gas.In the static experiment,the formaldehyde purification rate of the original and treated samples were 33.3% and 39.6% respectively in weak light conditions,and,38.6% and 49.2% in strong light conditions;in the dynamic experiment,the values were 69.9% and 77.1% in weak light conditions,and 77.1% and 85.5% in strong light conitions.It has proven that nanometer TiO₂can photodegrade formaldehyde in both strong light and weak light conditions.