To　study　the　frost　growth　rule　in　the　hot　channel　of　plate-fin　heat　exchangers　under　different　working　conditions,　a　frosting　model　based　on　Lewis　heat　and　mass　transfer　analogy　theory　is　established　and　then　combined　with　the　unsteady　heat　transfer　model　of　plate-fin　heat　exchanger.　First,　the　accuracy　of　the　model　is　verified　on　the　test　rig　for　frosting　visualization　on　flat　surface.　Then,　the　mass　and　starting　positions　of　frost　at　inlet　humid　air　flowing　speeds　of　0.8　m/s,　1.2　m/s　and　2.0　m/s　and　relative　humidities　of　60%,　70%　and　80%　are　compared,　respectively.　The　results　show　that　the　higher　the　air　velocity,　the　faster　the　frost　growth　rate　and　the　smaller　the　frost　area.　Also,　the　higher　the　relative　humidity　of　air,　the　faster　the　frost　growth　rate　and　the　larger　the　frost　area.　Meanwhile,　with　the　increase　of　the　frost　layer　thickness,　the　pressure　drop　of　the　channel　continues　to　increase,　and　the　efficiency　of　the　plate-fin　heat　exchanger　decreases.　When　the　average　thickness　of　the　frost　layer　accumulates　to　1.5　mm　in　the　hot　channel,　the　efficiency　of　the　heat　exchanger　decreases　by　about　10%.　©　2019,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.