The invention discloses a device and method for treating pulping wastewater by a catalyst and ozone. The device comprises a first-order reactor and a second-order reactor in which an active adsorption material load transition metal oxide catalyst is arranged, an exhaust receiving bottle, an ejector and a pump, wherein a first water inlet, a first water outlet and a reflux inlet are arranged on a tank body of the first-order reactor, a first ozone inlet and an exhaust outlet are arranged on a top cover, and an aerator is arranged in the tank body; a second water inlet, a second water outlet, athird water outlet and a sampling port are arranged on a tank body of the second-order reactor, and a second exhaust port is arranged on a top cover. The wastewater firstly enters the first-order reactor, is pumped into the ejector and the second-order reactor to be treated by the catalyst and the ozone so as to realize the effective degradation of organic matters in the wastewater. In the deviceand the method, the treatment effect is good, the ozone utilization rate is high, the operation and maintenance are convenient, the investment is low, the COD (Chemical oxygen demand) removal rate ismore than 60%, and the decolorization removal rate reaches more than 92%.