We study the different formulations of the hybrid vector FEM/BEM (Finite Element Method/Boundary Element Method) for 3-D scattering.It is shown that the condition number of matrices from different hybrid formulations varies greatly with different BEM formulations used

and therefore

the stability of the hybrid formulations varies correspondingly.Issues of combined testing function method and single testing function method for BEM are also discussed.We show that the combined testing function method can be viewed as the single testing function method.And the accuracy of the results obtained by the two methods is compared

which rectified the conclusion that accurate results can be obtained by the hybrid method only when the combined testing function method is employed.Based on the reliability

accuracy

and ability to immune to the corruption of interior resonance

the formulation of hybrid vector FEM/BEM for 3-D scattering is recommended.