A pilot-scale catalytic ozonation was conducted for the advanced treatment of dyeing wastewater from the secondary treatment process in a sewage treatment plant in Yulin, Guangxi Province. An iron-based catalyst derived from in-situ modification of iron shavings was used to investigate the performance of catalytic ozonation on COD and color removal of dyeing wastewater. The results showed that with the catalytic ozonation reactor and reaction conditions used in this study, the influent COD ranged from 40 to 60 mg·L-1, the color ranged from 80 to 120 PCU, and the pH value ranged from 6 to 9. The effluent water quality was stabilized to meet the Reusing Water for Textile Dyeing and Finishing (FZ/T 01107—2011) standard after undergoing this treatment process. Especially when the influent COD was maintained below 40 mg·L-1, the effluent COD could be reduced to 30 mg·L-1 or even 20 mg·L-1, and the effluent water quality met the Environmental Quality Standards for Surface Water (GB 3838—2002) Class IV water standard. The hydraulic retention time (HRT) on the treatment effect followed normal distribution. Under the experimental conditions, the optimal HRT for this wastewater was 60 min. The active components and the "micro-channel" structure of the iron-based catalyst were conducive to the combination of ozone and the catalytic components, and also promoted the release and action of hydroxyl radicals. Therefore, the ozone utilization rate was improved, with the O3/ΔCOD value remaining below 2.