Abstract: According to local standard,Meteorological Disaster Terminology and Classification of Hunan province，daily average temperature≤20℃（index I），≤22℃（index II）in 3 consecutive days or more was defined as the index of Autumn Low Temperature for conventional rice and hybrid rice，respectively.The earliest initial date of Autumn Low Temperature，the initial date for 50% year without Autumn Low Temperature，the initial date for 80% year without Autumn Low Temperature and daily frequency of Autumn Low Temperature were analyzed based on daily average temperature from 96 stations in Hunan province in September from 1951（the year of station construction）to 2010.The results showed that the earliest initial date of Autumn Low Temperature with index I was later 7-10 days than that of Autumn Low Temperature with index II Daily frequency of Autumn Low Temperature with index I was less than 5% in the first ten days and 10% in the middle ten days of September Daily frequency significantly increased in last ten days of September Daily frequency of Autumn Low Temperature with index II was less than 5% before September 8，then almost showed linear increase with time.The results indicated that the heading flowering stage delayed 3-5 days in north and center Hunan，so the medium late maturity rice was suggested to cultivate，instead of early maturing rice.

Key words: Autumn Low Temperature, Guarantee rate, Daily frequency, Full heading