Abstract: Based on the analysis to rainfall characters, the formulas to distinguish storm were raised taking both amount and intensity of rainfall as indexes, i. e., K = Pi, and K = P²/t - i₂t, which reflects the amount of rainfall in different time briefly, and is convenient for the analysis and calculation of storm. Meanwhile, the decision indexes and distinguish standard for storms by the standards of daily and interval rainfall or rainfall intensity were determined, they are as follows, 2 ≤ K < 7 for storm; 7 ≤K < 28 for great storm and K ≥ 28 for much greater storm.