Based on the standardized precipitation index data of 89 meteorological stations in southwest China (Sichuan Province, Yunnan Province, Guizhou Province, Chongqing) during 1961-2010, the probability and interval time were analyzed by employing the theory of run and the Copula function. The droughts with duration less than 4 months and the severity less than 3 account for 80% of all the droughts in southwest China. Drought types are mainly light within a month, moderate within a month, severe within a season and severe within inter-seasons. The frequency of occurring of drought with a duration less than 3 months and the severity less than 1 is higher in the eastern and western areas, and the central region has higher frequencies of occurrence of drought with a duration greater than 3 months and with severity greater than 1.5. Return periods of drought in eastern and western areas are longer than that of central region. More obvious spatial difference appears with longer duration and greater severity. The probability differences of the same drought type in different climatic types are within 0.05, indicating that there is no wide-range fluctuation in the occurrence probabilities of all the drought types as the time goes on.