Abstract: Using daily precipitation data for the period of 1951-2008 in Beijing,the study on the threshold values falling above the percentiles of the extreme events of precipitation,and the calculation of the threshold values with five methods,which are sorting,in terpolated,normal distribution transformation,square-root transformation,and cube root transformation,are researched in this paper.The results show that the evaluation of the threshold values using the method of square-root translation has the best effect in five methods.The mean of the threshold values on 30 year moving climatic period can be as the extreme events of daily precipitation in climate.