The　connected　automated　vehicle　(CAV)　platoons　are　expected　to　improve　the　operational　performance　of　the　transportation　system.　Existing　platoon　testing　processes　have　used　the　format　of　mixed　heterogeneous　platoons　(MHPs),　where　the　leader　vehicles　are　connected　human-driven　vehicles　(CHDVs)　and　the　follower　vehicles　are　CAVs.　The　impact　of　this　type　of　MHP　on　existing　highway　traffic　flow　is　more　complex　due　to　the　presence　of　human　drivers,　and　this　impact　has　yet　to　be　analyzed　and　quantified.　Therefore,　this　paper　takes　this　type　of　MHP　as　the　research　object　and　conducts　experiments　by　combining　driving　simulation　and　microscopic　traffic　simulation.　The　driving　behavior　of　the　driver　of　the　MHP＇s　leader　vehicle　is　incorporated　into　the　car-following　model　by　means　of　a　car-following　model　calibration,　and　an　impact　analysis　is　carried　out　in　terms　of　multiple　dimensions　of　stability,　efficiency,　and　ecological　aspects　of　the　mixed　traffic　flow　under　different　MHP　market　penetration　rates　(MPRs).　The　results　show　that　MHPs　weaken　the　oscillatory　effect　of　mixed　traffic　flow　and　improve　mixed　traffic　flow　stability.　The　MPRs　of　MHPs　are　proportional　to　the　road　capacity　and　average　speed　and　antipodal　to　the　average　travel　time.　Also,　the　MHPs　help　reduce　fuel　consumption　and　pollutant　emissions　(CO2,　CO,　NOx,　HC,　and　PMx)　during　traffic　operations.　This　study　can　provide　theoretical　support　for　the　future　large-scale　application　and　management　of　MHPs.　©　2024　Elsevier　B.V.