Abstract: Based on the data of thunderstorms in Mengla from 1957 to 2011,the climatological variation trends,temporal-spatial distribution and initial/ending dates of thunderstorms under different assurance ratios in the past 55 years have been analyzed in the light of climatic tendency coefficient,variation trends and assurance rations.The results show that the thunderstorms strike each month in Mengla,the thunderstorm days occur mostly from April to October,accounting for 90.2% of the year.The annual number of thunderstom days has a decreasing trend,mainly in summer and autumn,and there are decreases of about four thunderstorm days per decade in Mengla.For an assurance ratio of 80%,the initial thunderstorm date begins on January 12th and ends on December 16th.The initial thunderstorm date has a receding trend.For an assurance ratio of 5%,the initial thunderstorm date occurs on March 19th and the ending date occurs on October 7th.For an assurance ratio of 50%,the initial thunderstorm date occurs on January 31th and the ending date occurs on November 13th.