To　gain　an　in-depth　understanding　of　AAEMs　(alkali　and　alkaline　earth　metals)　transformation　during　biomass　gasification,　a　fixed-bed　reactor　is　built　to　simulate　the　CO2　gasification　at　500–900　°C.　The　influences　of　biomass　species,　gasification　temperature,　and　particle　size　are　examined.　The　results　show　that　the　AAEMs　release　follow　a　sequence　of　candlenut　wood　＞　wheat　straw　＞　corn　stalk.　The　alkali　metals　mainly　appear　as　water-soluble　inorganic　salts　and　the　contents　are　more　than　80%.　K　mainly　occurs　as　KCl　and　KClO4.　At　higher　temperatures,　K　could　combine　with　Al　and　Si　to　form　K(AlSi3)O8.　For　candlenut　wood,　a　bigger　particle　size　is　beneficial　to　the　transformation　of　water-soluble　K　to　organic　K.　For　candlenut　wood　with　centimeter-scale,　K　mainly　occurs　as　organic　K　in　the　biochar　during　600–700　°C.　When　the　gasification　is　carried　out　at　700　°C,　K　concentrates　at　the　center　and　its　content　is　even　higher　than　that　on　the　outer　surface.　While　for　biochar　samples　obtained　from　gasification　at　600　and　900　°C,　the　K　content　at　the　center　is　lower　than　that　on　the　outer　surface　due　to　the　continuous　outward　transformation　of　K　from　the　central　biochar.　©　2022　Energy　Institute