Chemical oxygen demand (COD) is a comprehensive index of organic pollutants in seawater, which is one of the most important items in marine environmental monitoring. The existing COD measurement methods are time-consuming and complex, which cannot meet the needs of online marine monitoring. This paper designs an integrating Microfluidic analysis system for COD using ozone chemiluminescence analysis. Different factors that influences on determination were optimized, including ozone and water flow rate, water temperature, salinity and filtration of the sample, etc. The experimental results have shown that this system can realize the analysis of 0.1~10 mg·L-1COD in seawater, the detection limit is 0.08 mg·L-1, and the measurement results are well consistent with the national standard method, Besides, it has the advantages of simple structure, short test time, meet the requirements of field analysis of seawater COD.