Abstract: Based on the daily minimum temperature data at 20 meteorological stations in Ningxia from 1961 to 2010, the first and the last frost dates were counted according to the frost indexes and statistics. Using statistical and climate diagnosis methods,the characteristics and change trend of the first and the last frost dates were analyzed. The results showed that the average first frost date came in early October while the average last frost date appeared in early May next year in Ningxia over the recent 50 years. However, it was not equal in the whole region. The earliest first frost date appeared in the mountain areas in the south, the next was in the dry areas in the middle and the latest first frost date appeared in the Yellow River irrigation area in the north. The last frost dates were sorted contrary with the first frost dates in the above three regions. In general,the average first frost date appeared late while the average last frost date came early in Ningxia in the last 50 years. The trend changes in the three regions showed no difference with the trend in the whole region. In 1960s and 1970s, the first frost dates were earlier and the last frost dates were later than the averages of the last 50 years. Since 1980s, the first frost dates were later or close to the average but the last frost dates were earlier or close to the average. The first frost date cumulative departures abruptly changed in 1974 for the whole region but the last frost date cumulative departures were changed in different years in the three regions which was in 1983 for the middle dry areas and the south mountain areas and was in 1982 for the Yellow River irrigation areas.

Key words: the first frost dates, the last frost dates, decade change, change test, change trend, Ningxia