The invention discloses a low-pressure catalytic oxidation reactor which comprises a reactor barrel. A light reflection flow guide barrel is arranged in the reactor barrel, a filler zone is arranged between the light reflection flow guide barrel and the reactor barrel, a water inlet pipe and a gas inlet pipe penetrate the portion, which is positioned on the lower portion of the reactor barrel, ofthe filler zone and are provided with water distributors and aerators, and the water distributors and the aerators are arranged at an opening in the bottom of the light reflection flow guide barrel. The low-pressure catalytic oxidation reactor has the advantages that wastewater and ozone can be directly fed into the light reflection flow guide barrel, the low-pressure wastewater can be fed into the light reflection flow guide barrel in a jet flow manner to be circulated in the light reflection flow guide barrel in a rotational flow manner, and can be sufficiently fused with the ozone, a drainpipe is arranged on the upper portion of the reactor barrel, the wastewater can flow out from the light reflection flow guide barrel, then sufficient reaction can be carried out on the wastewater andthe filler zone, and the wastewater can be ultimately drained from the drain pipe; the light reflection flow guide barrel is divided into a plurality of longitudinal oxidation zones by titanium dioxide catalysis plates, an ultraviolet lamp pole is arranged in the center of each oxidation zone, the catalysis plates are completely positioned in irradiation distances of ultraviolet light, the ultraviolet light can be reflected by the light reflection flow guide barrel, accordingly, illumination can be intensified, and the photocatalytic efficiency can be improved.