Abstract: With extremely cold days data from 16 stations in Hulun Buir during 1960—2014,the results showed that the geographical distribution of arctic days were unevenness and decreased from north to south;the forest area was more than pastoral area and rural area was the least. Interdecadal characteristics showed that arctic days in the 1960 s and 1970 s were the most,up to the 1960 s and the number of days significantly reduced in the 1980 s,at least in the 1990 s. At the beginning of 21 century,another arctic day slightly increased.The arctic days more appered in late December to late January,up to mid-January,followed by late January and gradual decreased after the beginning of spring in February.