To　investigate　the　mechanical　behavior　of　ultra-high-strength　concrete　(UHSC)　filled　steel　tubular　(UHSC-FST)　lattice　columns　under　eccentric　loading,　this　study　conducted　experiments　on　14　UHSC-FST　lattice　columns　with　varying　slenderness　ratios　and　eccentricities.　Failure　modes,　load-displacement,　load-strain,　and　lacing　tube　strain　curves　were　analyzed.　Results　revealed　distinct　failure　modes:　local　buckling　for　columns　with　a　slenderness　ratio　of　4　and　overall　buckling　for　those　with　a　slenderness　ratio　of　19.　As　slenderness　ratios　and　eccentricities　increased,　the　elastic　stage　proportion　decreased,　while　the　elasto-plastic　stage　proportion　grew.　The　lacing　tubes　in　all　specimens　exhibited　low　stress,　remaining　in　the　elastic　stage.　A　validated　finite　element　model　simulated　slenderness　ratios　from　4　to　49,　concrete　strengths　from　30　to　150　MPa,　and　eccentricities　from　0　to　1.5.　Simulations　showed　that　at　eccentricities　above　1　or　slenderness　ratios　≥　39,　the　influence　of　concrete　strength　on　ultimate　bearing　capacity　diminished.　Interaction　between　slenderness　ratio　and　eccentricity　affected　ultimate　capacity　but　was　limited.　Based　on　experimental　and　simulation　data,　existing　methods　for　calculating　stability　and　ultimate　capacity　were　verified　for　accuracy.　A　novel　calculation　method　suitable　for　UHSC-FST　lattice　columns　was　determined,　offering　high　precision,　alignment　with　physical　mechanisms,　and　practicality　for　engineering　applications.　©　2025　Institution　of　Structural　Engineers