The principle of set pair analysis (SPA) was introduced, the importantance of the value of i in SPA was pointed out, and the drawbacks of general approaches to the value of i was explained. Based on statistical test, a new approach to determine the reasonable value of i was precented attempted combined related coefficient of the set pair with kind coefficient. The results showed that the value of i in SPA is related to pair analysis to related coefficient of the set pair, variation coefficient and kind coefficient. The results about SPA should be helpful to hydrology and water resources.The reasonable outcome may be helpful in the field of hydrology and water resources.
