Abstract: A measure is taken based on secant method and tangent method to improve the computational method of eigenvalues with transfer matrix method on computer.In the new measure the references for searching the eigenvalues are the first k th powers of the eigen determinants(where k is larger than 1 0)instead of the determinants themselves,and the searching formulas of the existing method are modified correspondingly.As the range of the references for searching the eigenvalues is reduced considerably,the phenomenon of numerical overflow is eliminated forever.