Plenum　shape　and　position　play　a　significant　impact　on　the　heat　dissipation　performance　of　battery　pack　with　air-cooled　structure.　However,　the　existed　plenum　shape　and　position　are　simple.　In　this　work,　four　different　plenum　shapes　(slanted,　convex,　concave　and　stepped)　of　the　battery　thermal　management　system　(BTMS)　are　designed.　Then　the　influences　of　plenum　shapes　and　positions　(at　the　inlet,　outlet,　and　inlet　&　outlet)　on　the　heat　dissipation　performance　of　the　battery　are　investigated,　respectively.　Subsequently,　a　single　factor　analysis　is　performed　to　obtain　the　range　of　the　design　parameters　(H-in,　H-out,　R-in　and　R-out)　in　Design　6.　Finally,　a　multi-objective　optimization　of　Design　6　is　carried　out　to　further　improve　the　thermal　performance　of　BTMS.　Numerical　results　demonstrate　that:　1)　For　the　significant　improvement　of　the　cooling　ability,　convex　plenum　is　at　the　inlet　&　outlet　whereas　other　shape　ones　are　all　at　the　inlet.　2)　No　matter　where　it　is　at　the　inlet,　outlet,　or　inlet　&　outlet,　the　convex　plenum　achieves　the　excellent　cooling　effect　in　Z-　and　U-type　air-cooled　structures.　3)　Design　6　(convex　plenum　at　the　inlet　&　outlet)　exhibits　the　best　cooling　ability　among　all　plenum　shapes　and　positions.　4)　The　design　parameters　of　the　optimized　Design　6　are　H-in　=　17.9　mm,　H-out　=　19　mm,　R-in　=　2100　mm　and　R-out　=　2000　mm,　and　the　maximum　temperature　and　temperature　difference　respectively　achieve　a　35.06　%　(18.921　K)　and　76.98　%　(19.923　K)　reduction　under　such　optimized　design　parameter　settings　in　comparison　with　those　of　the　benchmark　(Design　9).