Deflection　monitoring　is　an　important　aspect　of　health　monitoring　system,　and　by　inclined　angle　measurement　the　structural　deflection　can　be　acquired　precisely　and　in　real-time　(RT).　The　relation　between　inclined　angle　and　deflection　was　deduced　in　the　case　of　cantilever　or　simply　supported　beam.　The　inclined　angle　was　fitted　and　then　integrated　to　obtain　the　diflection　with　the　help　of　MATLAB　and　the　result　was　compared　with　that　by　direct　deflection　measurement　in　the　test　of　a　steel　beam　under　loads.　A　health　monitoring　engineering　project　was　introduced　to　show　the　inclinometers＇　application　in　deflection　monitoring.　The　analysis　shows　that　the　deduced　relationship　between　incliner　angle　and　deflection　is　reasonable,　while　the　boundary　conditions　should　be　considered　with　regard　to　different　structures.　The　deflection　obtained　though　inclined　angle　integration　is　nearly　identical　with　the　deflection　measured.　If　inclinometers　are　used　in　the　health　monitoring　system,　then　the　RT　deflection　and　deflection　at　any　time　point　of　the　structures　can　be　obtained.