A simple, environmentally friendly and continuous flow method was developed for the determination of COD based on a flow injection analysis (FIA) system, in which a BDD electrode was employed as the detecting element. The structure and the electrochemical behavior of BDD were investigated by a scanning electron microscope, Raman spectroscopy, and cyclic voltammetry, respectively. The results demonstrated thatthe high-quality BDD film prepared here was suitable to be used as an electrode, with which the COD measurement could be conducted. The effect of several important experimental parameters, such as applied potentials, pH, flow rates, and supporting electrolyte concentrations, on the analytical performance was investigated. Under optimized testing conditions, the proposed method was successfully applied in the COD analysis of synthetic samples. The linear range and the detection limit were 2-175 and 1 mg L(-1), respectively. In addition, the COD values determined by the proposed method compared well with those analyzed bythe conventional method as demonstrated by small relative errors.