A　series　of　experiments　was　carried　out　to　investigate　the　frost　growth　on　a　vertical　flat　cryogenic　surface　under　natural　convection.　The　results　show　that　when　the　cold　surface　temperature　below　a　certain　value,　the　frost　layers　tend　to　grow　from　the　top　downwards　along　the　cold　surface.　The　vertical　growth　velocity　and　frost　layer　thickness　would　be　influenced　by　the　air　relative　humidity　significantly,　whereas　the　influences　of　cold　surface　temperature　are　very　weak.　The　growth　patterns　of　frost　layers　in　vertical　direction　can　be　classified　into　nonlinear　growth　and　linear　growth.　When　the　frost　layer　growth　pattern　is　single　dendritic　growth,　its　growth　is　linear,　frost　layers　have　quite　similar　vertical　growth　velocities　if　air　relative　humidity　is　the　same　in　different　experiments.　When　there　are　clusters　of　frost　crystals　grow　from　the　bottom　up　at　the　front　ends　of　the　main　frost　layer,　the　growth　pattern　is　non-linear,　the　non-linear　growth　slows　down　the　vertical　growth　velocity.　The　growth　pattern　of　frost　layer　at　the　early　stage　has　essential　effects　on　frost　deposition　in　the　long　run,　which　can　determine　the　mass　transfer　or　at　least　the　frost　thickness　of　the　frost　deposition　process.　©　2018　International　Heat　Transfer　Conference.　All　rights　reserved.