The process of decorating interior spaces often produces substances that are harmful to the human body, which seriously spoils the decorating experience. Photocatalyst is the oxidant of nanometer titanium dioxide. It cannot be oxidized by itself. This article aims to discuss photocatalysts and interior and exterior design. When there is light in the room, the photocatalyst will fully integrate with the light, which has a strong catalytic and degrading effect. This can degrade indoor formaldehyde and other pollutants while also having a sterilization effect. The principle of the photocatalyst is to absorb ultraviolet rays in light. When impurities appear in the air, they are destroyed by the photocatalyst, and the impurities are converted into substances that are harmless to the human body. We tested the formaldehyde and SO2 content in the room after the photocatalysis of titanium dioxide, and analyzed the photocatalyst and decoration design in indoor public spaces. The research results showed that the effect of the photocatalyst is about 20% better than the traditional explanation. Functionally, it can deodorize toilets, garbage, etc., and the effect is very obvious.