Abstract <p>Currently, most online monitors available on the market to detect the total chromium (<b>TCr</b>) in water mostly employ potassium permanganate or potassium persulfate oxidation-1,5-diphenylcarbazide (<b>DPC</b>) spectrophotometry. However, some problems still exist, such as the interference of residual oxidants with the determination, high temperature and time-consuming oxidation digestion reaction, high consumption of multiple chemical reagents, and complicated operation. Thereby, this study proposed a novel method combining ozone-based advanced oxidation processes with DPC spectrophotometry for the rapid and environmentally friendly determination of TCr in water. Based on a novel experimental device designed for the determination of TCr, the effects of reaction solution volume, pH, reaction time, ozone flow, and ultraviolet light intensity on the oxidation rate of TCr were investigated. Concurrently, the influence of the solvent of the chromogenic agent, chromogenic acidity, amount of chromogenic agent, and chromogenic time on the determination outcomes of TCr were also explored and optimized. Results revealed that under the optimized process conditions, within the concentration range of 0–1.25 mg/L, the proposed method manifested outstanding linearity (<i>R</i>² = 0.9998), precision, indication error, method detection limit, and conversion rate were 1.14, 1.17%, 0.0007 mg/L, and 98.99%, respectively. This will be a promising and alternative method for routine analysis or online monitoring of TCr in water.</p>