Abstract: The frost characteristics in Taiyuan city were analyzed based on the daily minimum temperature data in Taiyuan Meteorological Station from 1951 to 2008,by using the methods statistics,cumulative filter and non-parametric respectively.The results showed that the first light frost was occurred in October 14th,and the last light frost was in April 15th.The average free-frost period was 182 days.Comparably,the first moderate and severe frost delayed 9 days and 23 days,the last ones advanced 11 days and 24 days.The average free-frost period was extended 20 days and 47 days.In totally,the first frost changed complexly,the last frost was delayed during 1950s to 1970s and advanced since 1980s.The average free-frost period was shortened during 1950s to 1970s and extended since 1980s.Generally,the first frost delayed and last frost advanced,and the average free-frost period was extended.The occurring frequency of abnormal first or last frost event took up 5～15%,most of them were in the years of 1950s-1970s.The abnormal first light frost event usually had little impacts on crops and cabbage.But the cabbage would suffer from freezing injury with the abnormal first moderate or severe frost.The abnormal last frost could affect seedling in spring.Winter wheat suffered from the frost damage one time in each 5 years,and the risk stage was 5 days after jointing.

Key words: Daily minimum temperature, Daily minimum temperature, First and last frost, Unusual frost criterion, Cumulative filter method, Taiyuan city