Abstract: According to the importance of storage state and the operation policy of reservoir or reservoir-group for satisfying the water requirements of regional water-supply system,the regional drought identification procedure,which is taken as the key judgment parameters,the sum of the initial time-period storage of reservoir and the inflow within the period,and the goal water requirement of water-supply system are proposed.The procedure indicates the drought and non-drought status of the water-supply system by the positive and negative sign of the difference of the above two key parameters.To make the comprehensive analysis of the characteristics of the regional drought,such as the distribution pattern of the drought and non-drought duration, the transfer probabilities,the recurrence interval of drought,etc.,we,from various research aspects,take a real water-supply system as example.Both the simulating and statistical method and probability analysis method are applied to the drought duration study.Meanwhile,the distinction of the traits and the computing results of two methods and their causes are pointed out.