Base　on　inclinometers　and　the　orthogonality　of　the　mode　shape,　a　method　of　bridge　deflections　testing　is　given.　The　method　includes　the　process　of　determining　the　inclinometer＇s　position　and　number.　Base　on　the　analysis　of　the　deflections　contributions　of　each　mode　for　the　given　section　under　the　different　loading　cases,　the　mode　order　for　fitting　has　been　confirmed.　The　number　of　inclinometers　must　be　equal　or　larger　than　the　number　of　modes　using　for　fitting.　The　inclinometers　should　be　installed　on　the　oblique　peaks　of　each　mode.　Using　the　special　characters　of　the　symmetrical　bridge　modes,　inclinometers　should　be　laid　on　the　oblique　peaks　of　odd　modes　and　symmetrically　by　the　mid-span.　Finally,　based　on　three　general　bridge　types,　the　modes　order　and　inclinometers　positions　are　determination　and　the　fitting　effect　are　checked　under　two　cases.　The　results　indicate　that　the　deflections　of　mid-span　section　can　be　fitting　well　using　several　odd　modes　with　the　inclinometers　on　the　oblique　peaks　of　each　mode.