Based on the data of 48 stations in eastern Yunnan during 1959-2006 and year 2008, we assessed the temperature, precipitation and other disastercausing factors of the freezing disaster in Yunnan from January 14 to February 28, 2008, which caused significant economic losses and casualties. According to the number of freezing days and the supplemental data of the average minimum temperature in the process, we have constructed a frost freezing disaster estimation composite index. A comprehensive assessment is conducted on the frost freezing disaster on the basis of the fuzzy information distribution theory and the method of return period of right probability extremum. The results show that comparing with the same period in many years, the maximum temperature of eastern Yunnan in 2008 is 4.7 ℃ lower, breaking the lowest historical record; the average temperature, 2.5 ℃ lower—the second lowest historical record; the number of cloudyday, 10.3 days more—a 90% increase and breaking the maximum historical record; the days of precipitation, 8.7 days more—a 78% increase which also breaks the maximum historical record; the figure of intensity index of the frost freezing disaster breaks the maximum historical record as well. The frost freezing disaster in Yunnan from January 14 to Feburary 28 in 2008 is the extraordinarily serious frost freezing disaster compared to the same period within 100 years；the figure of intensity index of the disaster is also the maximum historical record in winter in Yunnan. The disaster is the extraordinarily serious frost freezing disaster in winter within 50 years.