A tubular photocatalytic air purifier was designed on the basis of photocatalytic purification theory. With formaldehyde as experimental pollutant, its purification effect was compared with that of the traditional plate type reactor. The results show that the purification effect of the tubular reactor is better than that of the plate type reactor, and the degradation efficiency increases by 14%. Orthogonal tests show the significance level of the factors affecting purification efficiency is environmental temperature > initial concentration of formaldehyde >P25 TiO₂ load. The best catalytic conditions of the tubular photocatalytic air purifier are environmental temperature 25℃, P25TiO₂ capacity 1 mg/cm² and initial concentration of formaldehyde 0.7 mg/m³. Under the best catalytic conditions, the degradation rate of formaldehyde can achieve 89% within 120 min.