The　initial　rotational　stiffness　of　connections　is　important　for　the　design　of　semirigid　frames.　However,　most　current　studies　on　steel　beam　to　concrete-filled　steel　tube　column　connections　with　bidirectional　bolts　are　based　on　experimental　tests,　and　theoretical　analysis　and　numerical　analysis　are　rarely　reported.　As　a　result,　there　is　no　suitable　analytical　model　for　calculating　the　initial　stiffness　of　the　connection.　Based　on　the　component　method,　this　paper　proposes　an　analytical　model　to　predict　the　initial　stiffness　of　the　connection.　It　is　considered　that　the　connection　rotation　is　mainly　induced　by　deformations　of　the　endplate　in　bending,　column　flange　in　bending,　bolts　in　tension,　and　panel　zone　in　shear.　Moreover,　the　effects　of　the　endplate　in　bidirectional　bending　and　bolt　pretension　are　taken　into　consideration.　Then,　the　prediction　results　based　on　the　proposed　analytical　model　are　compared　with　experimental　results　to　verify　its　accuracy,　and　comparison　results　indicate　that　the　proposed　analytical　model　can　predict　the　initial　rotational　stiffness　of　steel　beam　to　concrete-filled　steel　tube　column　connection　well.　In　addition,　bolt　diameter　and　endplate　thickness　are　the　most　influential　parameters　that　affect　the　initial　stiffness　of　the　connection.　It　also　provides　a　way　for　such　connections　to　be　designed　as　rigid　connections.　Finally,　the　proposed　analytical　model　can　be　applied　with　good　precision　in　elastic　analysis　and　serviceability　calculations　in　the　design　of　semirigid　steel-concrete　composite　frames.　It　can　be　applied　to　four　types　of　connections:　stiffened　extended　endplate　connections,　nonstiffened　extended　endplate　connections,　flush　endplate　connections,　and　T-stub　connections.　The　proposed　analytical　model　saves　substantial　resources　and　workload　in　experiments　and　simulations.　©　2018　American　Society　of　Civil　Engineers.