A　mathematical　model　of　the　plate-fin　heat　exchanger　filled　with　catalyst　(CFPFHX)　is　established　to　investigate　the　continuous　cooling　process　coupled　with　ortho-para　hydrogen　conversion　at　42-70　K.　The　flow　and　heat　transfer　performance　and　the　efficiency　of　ortho-para　hydrogen　conversion　in　the　CFPFHX　are　quantitatively　evaluated,　and　the　effects　of　the　structural　parameters　on　the　flow　and　heat　transfer　coupled　with　orthopara　hydrogen　conversion　are　analyzed.　The　results　show　that　the　Elovich　model　is　the　best　existing　kinetic　models　of　ortho-para　hydrogen　conversion　with　an　average　relative　deviation　of　1.8%.　The　Colburn　heat　transfer　factor　(j　factor)　of　the　hot　side　of　the　CFPFHX　is　4.3　times　that　of　the　plate-fin　heat　exchanger　(PFHX),　and　the　thermal　enhancement　factor　(TEF)　of　the　hot　side　is　37.7%　of　that　of　the　PFHX.　Meanwhile,　for　the　CFPFHX,　the　j　factor　and　the　TEF　of　the　hot　side　under　different　structural　parameters　are　always　about　8-10　times　and　68%-93%　of　that　of　the　cold　side　respectively.　Therefore,　the　CFPFHX　can　ensure　the　flow　and　heat　transfer　performance　and　realize　the　ortho-para　hydrogen　continuous　conversion.　And　a　fin　with　the　larger　flow　area　(high　fin　height,　wide　fin　spacing　and　small　fin　thickness)　has　a　better　flow　and　heat　transfer　performance　and　ortho-para　hydrogen　conversion.　The　outlet　para-hydrogen　ratio　y(p-H2)(out)　and　the　mass　space　velocity　vm　in　the　CFPFHX　have　an　approximate　linear　trend.　When　mass　space　velocity　v(m)　＜=　0.6589　kg/(m(3).s),　the　outlet　para-hydrogen　ratio　y(p-H2)(out)　can　meet　the　requirement　at　42-70　K.　Above　all,　the　mechanism　of　flow　and　heat　transfer　coupled　with　ortho-para　hydrogen　conversion　is　revealed　for　the　first　time　in　this　study,　which　can　provide　a　theoretical　guidance　for　the　application　of　the　integrated　technology　in　large　scale　hydrogen　liquefaction　process.　(C)　2021　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.