The colloidal titanium dioxide was prepared by sol-gel method and the ferric ion was modified, get the catalyst Fe3+/TiO2. The effects of residence time,initial concentration of Pr thioether and Pr mercaptan, relative humidity and other factors on the photocatalytic degradation of propylthiourea and the impact of propanethiol. The study found that the residence time in the 3.5∼4.5 s, the relative humidity of 45%∼50% degradation best, and the initial concentration of degradants substance was controlled within 200mg/m3 after pretreatment, and the degradation effect was good.