A　modal　test　was　carried　out　on　a　120m　span　concrete　filled　steel　tubular　arch　bridge　under　operational　conditions.　The　moving　traffic　load　is　considered　as　uncorrelated　white　noises　at　various　points　of　the　road　surface　and　the　test　is　of　the　type　of　multi-input　multi-output　(MIMO).　The　modal　parameters　are　identified　by　Global　Rational　Fraction　Polynomials　(GRFP)　method,　a　frequency　domain　method.　In　order　to　taking　the　mobile　nature　of　the　traffic　load　into　consideration,　a　multi-input　NExT　method　:is　utilized　to　retrieve　the　frequency　response　function　needed　by　GRFP.　A　proof　of　the　NExT　method　in　the　case　of　multi-input　case　is　also　provided　in　this　paper.