Quantitative　measurements　were　carried　out　of　the　dendrite　frost　crystal　growth　under　natural　convection　conditions　on　a　frozen　water　drop　sitting　on　a　cold　surface　whose　temperature　is　as　low　as-190　degrees　C　to　study　the　effects　of　cold　surface　temperature,　wet　air　state　and　original　water　drop　size.　In　order　to　classify　the　influences　of　different　cold　surface　temperature　regions,　the　frost　crystal　dendrite　growth　of　both　ordinary-low　and　cryogenic　cold　surface　temperatures　were　investigated.　It　was　found　that　the　cold　plate　surface　temperature　has　a　direct　influence　on　frost　formation　mechanism.　Decreasing　the　cold　surface　temperature　for　ordinary-low　cold　surface　temperatures　will　enhance　and　for　cryogenic　cold　surface　temperatures　will　suppress　the　frost　crystal　dendritic　growth　of　the　frozen　water　drop.　The　measurements　disclosed　that　the　length　of　the　longest　frost　crystal　dendrite　grows　almost　linearly　with　time,　esp.　in　the　early　stage.　The　effects　of　the　water　drop　sizes　on　the　longest　frost　crystal　dendrite　growth　become　more　and　more　obvious　as　the　cold　surface　temperature　decreases.　The　influence　of　air　relative　humidity　on　the　frost　crystal　dendrite　growth　is　something　similar　to　that　of　air　temperature　under　given　conditions,　since　their　change　both　changes　the　absolute　air　humidity.　A　very　peculiar　phenomenon,　i.e.　the　influence　of　wet　air　state　on　frost　crystal　dendrite　growth　is　not　monotonous,　was　observed.　These　findings　are　important　for　understanding　and　studying　the　frost　formation　and　growth,　especially　the　initial　frost　formation　period,　on　low　temperature　surfaces.