Abstract: To determine whether the exponential distribution curve is suitable for the selection of sample series, the theoretical analysis was conducted based on the similarity between the exponential distribution curve and probability density curve of different samples. Combined with the instance, exponential distribution curve can fit the probability density histogram of different sampling methods. Results show that the annual maximum value sampling do not fit for exponential distribution curve. When the probability density curve of the sample shows as “Na” glyph, the annual multi-sampling method can use the exponential distribution curve. Otherwise, it cannot.