Different　from　conventional　cold　leg　safety　injection,　a　newly　designed　reactor　type　CAP1400　directly　connects　the　injection　pipeline　of　the　emergency　cooling　system　with　the　pressure　vessel.　However,　these　structures　have　been　found　to　potentially　have　adverse　effects　on　the　pressure　vessel.　This　paper　employs　both　physical　experiment　and　numerical　analysis　to　investigate　the　dynamic　oscillating　load　and　the　structural　response.　A　1:9　scale　model　is　adopted　for　the　experimental　section.　The　uncertainty　of　the　measurement　quantities　is　within　3%.　The　CFD　code　and　the　FEM　code　are　used　to　simulate　the　transient　fluid　flow　and　solid　structure　deformation,　respectively.　The　sequential　coupling　method　is　used　for　the　thermal-fluid-solid　coupling　calculation.　The　overall　error　of　the　calculation　is　within　±10%.　The　result　shows　that　the　fluctuation　of　the　physical　quantity　near　the　wall　is　caused　by　turbulence　eddy　and　thermal　mixing,　and　the　flow,　heat　transfer　and　structural　deformation　near　the　wall　of　the　pressure　vessel　are　closely　coupled.　The　effect　of　the　turbulence　eddy　can　be　seen　within　the　entire　range　of　frequency　measured,　while　that　of　the　thermal　mixing　can　be　seen　only　within　the　low　frequency　range.　The　influence　law　of　the　loop　flow　ratio,　the　flow　rate　of　the　downcomer　and　the　loop　temperature　difference　in　the　structural　response　are　obtained.　Through　the　research　of　this　paper,　the　law　of　interaction　between　the　thermal-fluid　load　and　the　structural　response　under　direct　safety　injection　is　more　deeply　understood.　Thus,　it　provides　a　design　reference　for　the　safety　of　reactors.　©　2022