Electrochemistry is an efficient, fast and green method for the COD removal of sewage. The electrochemical treatment process of sewage containing polymer in an oilfield produces some reactive intermediates such as H2O2 which can remove COD by indirect oxidation. It is very difficult to detect accurately and quantitatively with general methods because of the trace H2O2 in the process of electrochemistry. Thus, we need a method of high-sensitivity to measure the amount of H2O2 to guide the control process of electrochemical treatment; Ti and 5-Br-PADAP with H2O2 can form a stable colored ternary complex at pH 1~1.5, and there is an obvious absorption peak of this ternary color system at about 561 nm. Within the range of 02～10 μmol·L-1 H2O2 and sticking to Beer-Lambert Law, a method of spectrophotometry can be established for determination of trace reactive intermediates about H2O2 in the process of electrochemical treatment of sewage. The UV spectra of 5-Br-PADAP(B), binary complexes Ti(Ⅳ)-B and ternary complexes of Ti(Ⅳ)-B-H2O2 is studied and the determination method of trace H2O2 is proposed in this paper. Here are innovations of this paper: The factors of influencing the formation and stability of ternary complex system of Ti(Ⅳ)-B-H2O2 are the order of adding reagents, pH, the amount of anhydrous ethanol, heating temperature and time and the ratio and amount of Ti(Ⅳ)-B with UV spectroscopy. The experimental conditions for the accurate detection and quantification of trace H2O2 are obtained: pH 1.0~1.5, 50% of ethanol, heated in water bath at 50 ℃ about 20min, Ti(Ⅳ) and B solution mixed at the equal molar ratio, The order of adding reagents: 2 mL of various concentrations of these standards H2O2 solution, 3 mL of anhydrous alcohol, 1 mL of 0.32 mol·L-1 HCL, 2 mL of pH 1.5 HCl-KCl buffer solution, 2 mL of Ti(Ⅳ)-B solution to a 10 mL volumetric flask, and dilute with 0.32 mol·L-1 HCL solution to the mark line of volume. The method is easy, rapid, reproducible, cheap and high sensitive, and it obtains satisfying results in practical applications.