A highly sensitive new method was established to determine trace bromate in water. In acid solution, excessive iodide ions were oxidized into I3- by bromated. With phosphoric acid-sodium dihydrogen phosphate buffer solution, and nonionic surfactant OP, the anion I3- reacted with Victoria blue BO (VPB BO) to form a kind of brilliant blue ion-association complex, and then use spectrophotometric method to measure trace bromate in water. At 580nm wavelength, the apparent molar absorptivity of associated complex was up to ten power of five. High recoveries were got by using this method to measure the trace bromate in drinking water. VPB BO spectrophotometric method had many advantages such as high sensitivity, simply operation, high-speed, accuracy in the measurement of trace bromate in water.