Nanometer TiO2 particles were prepared with Ti(SO4)2 as precursor using the precipitation-sol method, and its photocatalytic degradation experiments of formaldehyde were carried out. Influence of preparation conditions of TiO2 on photocatalytic degradation performance was studied. The results showed that degradation rate of formaldehyde attained 78% in 6 hrs at the concentration of Ti(SO4)2 0.05 mol/L, hydrolization temperature 80℃ and time 4 hrs, pH=2 for congregatation with 0.10 mol/L KOH, maturation temperature 90-100℃...