Abstract: Synchronous or quasi-synchronous sea-land-air observations were conducted using advanced sea ice,atmospheric and marine instruments during China's First Arctic Expedition.Based on the precious data from the expedition,it is found that in the Arctic Ocean,most part of which is covered with ice or is mixed with ice,various kinds of sea fog formed such as advection fog,radiation fog and vapor fog.Each kind has its own characteristic and mechanics of creation.In the southern part of the Arctic Ocean,due to the sufficient warm and wet flow there,it is favor able for advection fog to form,which is dense and lasts a long time.On ice cap or vast floatingice,due to the strong radiation cooling effect,stable radiating fog is likely to form.In floating ice area there forms vapor fog with the appearance of masses of vapor from a boiling pot,which is different from shor-tlasting land fog.The study indicates that the reason why there are many kinds of sea fog form in the Arctic Ocean is the complicated cushion and the consequent sea-air interaction caused by the sea ice distribution and its unique physical character istics.Sea fog is the atmospheric phenomenon of sea-air heat exchange.Especially,due to the high albedo of ice and snow surface,it is difficult to absorb great amount of solar radiation during the polar days.Besides,ice is a poor conductor of heat; it blocks the sea-air heat exchange.The sea-air exchange is active in floating ice area where the ice is broken.The sea sends heat to the atmosphere in form of latent heat;vapor fog is a way of sea-air heat exchange influencing the climate and an indicator of the extent of the exchange.The study also indicates that the sea also transports heat to the atmosphere in form of sensible heat when vapor fog occurs.