In　order　to　improve　the　performance　of　plate-fin　heat　exchanger,　a　three-dimensional　numerical　investigation　of　fluid　flow　and　heat　transfer　characteristics　in　plain　fins　of　plate-fin　heat　exchanger　was　performed　using　CFD　software.　The　effect　of　configuration　and　average　inlet　Re　number　on　the　characteristics　in　plain　fins　was　studied.The　results　show　that　the　temperature　of　fluid　adjacent　to　the　wall　is　higher　while　that　of　central　fluid　is　lower　when　fluid　is　heated.　There　is　obvious　temperature　gradient　in　the　fluid.　It　is　higher　near　the　wall　while　lower　in　the　central　fluid.　The　values　of　j-　factor　and　f　-factor　all　increase　with　the　height　and　spacing　of　plain　fins.　With　the　increase　in　fin　thickness,　the　heat　transfer　performance　of　plain　fins　is　intensified　to　some　extent　while　there　is　an　optimum　value.　The　numerical　results　are　in　good　accordance　with　the　reported　experimental　values.　The　results　provide　the　theoretical　basis　for　the　optimum　design　of　plate-fin　heat　exchangers.