Micro-observation　of　frost　formation　and　deposition　processes　on　a　vertical　hydrophobic　cold　surface　was　made　under　free　convection　conditions.　The　formation　and　shape　variation　of　frost　crystals　during　the　initial　period　are　described　and　the　frost　thickness　variation　with　time　on　both　hydrophobic　and　plain　copper　cold　surfaces　are　presented.　The　various　influencing　factors　are　discussed　in　depth.　The　mechanism　of　frost　formation　on　hydrophobic　surfaces　was　analyzed　theoretically.　This　revealed　that　increasing　the　contact　angle　can　increase　the　potential　barrier　and　restrain　crystal　nucleation　and　growth　and　thus　frost　deposition.　The　experimental　results　show　that　the　initial　water　drops　formed　on　a　hydrophobic　surface　are　smaller　in　size　and　remain　in　the　liquid　state　for　a　longer　time　compared　with　ones　formed　on　a　plain　copper　surface.　It　is　also　observed　that　the　frost　layer　deposited　on　a　hydrophobic　surface　is　loose　and　weak.　Though　the　hydrophobic　surface　can　retard　frost　formation　to　a　certain　extent　and　causes　a　looser　frost　layer,　our　experimental　results　show　that　it　does　not　depress　the　growth　of　the　frost　layer.