In　this　paper,　a　numerical　investigation　is　performed　for　three-stage　heat　exchangers　with　plain　plate　fins　and　slit　fins　respectively,　with　a　three-dimensional　laminar　conjugated　model.　The　tubes　are　arranged　in　a　staggered　way,　and　heat　conduction　in　fins　is　considered.　In　order　to　save　the　computer　resource　and　speed　up　the　numerical　simulation,　the　numerical　modeling　is　carried　out　stage　by　stage.　In　order　to　avoid　the　large　pressure　drop　penalty　in　enhancing　heat　transfer,　a　slit　fin　is　presented　with　the　strip　arrangement　of　＂front　coarse　and　rear　dense＂　along　the　flow　direction.　The　numerical　simulation　shows　that,　compared　to　the　plain　plate　fin　heat　exchanger,　the　increase　in　the　heat　transfer　in　the　slit　fin　heat　exchanger　is　higher　than　that　of　the　pressure　drop,　which　proves　the　excellent　performance　of　this　slit　fin.　The　fluid　flow　and　heat　transfer　performance　along　the　stages　is　also　provided.