Abstract: A method of multi-frequency calculation is proposed by using Burton-Miller improved boundary integral equation.The high singular integral in the Burton-Miller equation is transformed into a weakly singular integral form and Burton-Miller improved boundary integral equation is obtained.The Green function of the equation is expanded by Taylor series and the wavenumber is separated from the equation so that the calculation matrix in dependence of wave number is expressed as the matrix series associated with wavenumber.The numerical analysis shows that not only this method guarantees the uniqueness of solution in the range of full wavenumber,but also can save a lot of time and improve the calculation efficiency when there are many frequency points to be calculated.