The　mechanical　behavior　of　concrete-filled　steel　tube　(CFST)　subjected　to　lateral　impact　was　studied　by　drop　hammer　test　and　finite　element　method　(FEM).　Lateral　deformation　occurred　when　the　midspan　of　CFST　was　impacted　by　a　drop　weight.　Two　plastic　hinges　were　formed　in　the　mid-span　and　near　the　fixed　support,　respectively.　The　numerical　and　experimental　results　were　compared　to　ensure　that　the　numerical　model　was　reasonable　for　investigating　the　stress　development,　damage,　and　inertial　force　of　the　CFST　column.　The　effects　of　the　impact　velocity,　impact　mass,　cross-sectional　steel　ratio,　and　boundary　conditions　on　the　inertial　force　of　the　CFST　column　were　analyzed.　During　the　impact　process,　the　maximum　stress　was　at　the　steel　tube　part　of　the　impact　location　and　the　fixed　support,　while　the　other　parts　were　still　in　the　elastic　or　elastoplastic　stages.　The　region　under　restraint　at　the　fixed　end　of　the　CFST　column　exhibited　the　first　signs　of　concrete　core　damage　under　tension,　followed　by　the　region　near　the　location　of　the　impact　at　midspan.　At　the　peak　impact　force　(Fp),　the　impact　velocity　had　a　considerable　influence　on　the　distribution　of　inertial　force　of　CFST,　while　the　impact　mass　and　cross-sectional　steel　ratio　had　no　discernible　impact　on　the　inertial　force　at　the　Fp,　and　boundary　conditions　had　little　impact　on　the　distribution　of　inertial　force.　Based　on　a　research　of　the　inertial　force　at　the　Fp,　a　simple　mechanical　model　of　the　inertial　force　was　built.