Formaldehyde, as a main indoor pollutant, is a serious hazard for human health. Here the experimental results of dielectric discharge, together with photo-catalysis to treat formaldehyde, were presented. The modified photocatalyst was loaded onto the electrode surface for degradation of formaldehyde in an artificially enclosed room. The effect of catalyst quantity, inlet rate, temperature, humidity and other process variables were examined in order to explore the relative purification factors of plasma cooperated with photo-catalysis. It is found that formaldehyde degradation efficiency is proportional to photo-catalyst quantity, and reciprocal to gas inlet rate and humidity. Experimental results confirm that plasma discharge combined with photo-catalysis can significantly improve the treatment efficiency of formaldehyde compared to a single plasma discharge. This research may form a basis for practical development of an efficient, low-power-cost, and relatively comprehensive indoor pollutant purification system.