Cobaltous oxide modified activated carbon was prepared by pre-treatment, ultrasonic immersing and calcination. Through thermal gravimetric analysis, the TG temperature for cobaltous oxide modified activated carbon was 410℃, which increased for 30℃ compared with normal activated carbon. Through XRD analysis, the adsorption peaks of cobaltous oxide modified activated carbon appeared at 2θ values of 20.9°, 37.1° and 43.0°. Furthermore, the surface crystalline of activated carbon was doped with the diffraction peak of CoO cubic crystal. Scanning with SEM, the surface defects of activated carbon increased due to the presence of CoO particles. Under certain conditions, 87.95%-96.18% decolorization efficiency and 78.31%-89.70% COD removal could be achieved by using microwave catalytic degradation of acid and cationic dyes in the presence of cobaltous oxide modified activated carbon, and the degradation process could be simulated by first order kinetics. This research proved that dye wastewater could be successfully removed by microwave catalytic degradation in the presence of cobaltous oxide modified activated carbon.