Abstract: Determining the aperiodicity parameter α (equivalent to the familiar coefficient of variation) is important for calculating the possibility of large earthquake occurrence. Considering the deviation between the estimate values of α from small sample of earthquake sequences and the actual values of α， this paper presents a new method for computing α. Firstly, a large number of estimated values of α for small samples from earthquake sequences are calculated by maximum likelihood estimate method， and then the estimated values are standardized and statistically analyzed. Finally, based on the 39 recurrent earthquake sequences, a general value of α is given (α=0.34), and the physical meaning and application of the value are also discussed.