The final product of stable chlorine dioxide collected contains some interfering substances for determining its concentration with ordinary method.A distillation-titration method has been developed.Chlorine dioxide is distilled from H₂SO4 solution and absorbed by KI solution.Then yield I₂ is determined with Na₂S₂O₃.NaClO₃ and NaClO₂ have no interferance.The concentration of stable chlorine dioxide can be determined rapidly and conveniently.The choice of acid,time of distillation,pH of the solution and the repetition rate of this method are discussed.