HCHO removal from indoor air was usually slow and inefficient due to the low concentration but persistent release, inadequate oxidation and less efficient catalysts at room temperature. PEC (photo-electro-catalysis) can better remove pollutant than PC (photocatalysis) or EC (electro-catalysis), but was rarely used directly in indoor air purification, because often aqueous electrolyte was not considered in indoor air purification reactor. Theoretically, removing HCHO in indoor air by PEC is possible, the question is how to integrate gas phase reaction with electric field and electrolyte. In this article, using copper anode in a thin film liquid electrolyte and high activity Pt/TiO2-ZnO cathode, efficient HCHO removal was realized by photo-electro-catalytic oxidation. The nano catalyst was prepared by sol-gel method and loaded on stainless steel mesh as cathode. Its structure, morphology and photocatalytic properties were characterized. The effect of Pt loading and/or external resistances on the removal efficiencies were investigated. Within 120 min of reaction time, 74% HCHO (0.16 mg/m(3), in 5.56.10(-3) m(3) air volume) was removed using 36 cm(2) cathode loaded with 4.16.10(-3) mg/cm(2) catalyst, while only 42% and 53% was removed respectively in PC and EC using the same catalyst and reactor.