Total 47species and varieties of diatoms from 27genera were found from 48samples of the Core ARC5- C01in the Chukchi Sea.The eleven dominant diatoms are Actinoptychus undulates(Bail.)Ralfs,Biddulphia aurita (Lyngbye)Brebisson et Godey,Coscinodiscus argus Ehrenberg,Coscinodiscus curvatulus Grunow,Coscinodiscus oculus Ehrenberg,Fragilariopsis oceanica (Cleve)Hasle,Fragilariopsis sp.,Paralia sulcata (Ehrenb.)Cleve, Thalassiosira antarctica Comber,Thalassiosira leptopus(Grun)Halse et G.Fryxell and Thalassiosirasp.Cluster analysis shows that the studied core can be subdivided into 3zone and 2subzone.The paleoclimate of diatom zone I1 is relatively warm represented by the dominant species of Actinoptychus undulates and Paralia sulcata;both Thalassiosira antarcticaand Azpeitia noduliferaincreased at the diatom zone I2which demonstrated cold and warm water mass mixing;Fragilariopsis oceanicadecreased dramatically at the diatom zoneⅡwhich showed that the surface and the underlying water exchange slowly;At the diatom zoneⅢ,the significant phenomena is that warm water species decreased and polar species increased and at 550cal.a BP,Bacteriosira bathyomphala appeared with a high value which indicated the sediments formed under harsh conditions due to the global cooling(Little Ice Age)with more ice cover in the research area and relatively reduced influence of the warm Bering Sea waters.