To ensure the effectiveness of the rainfall early-warning index threshold in early warning within a certain period, an analysis of existing methods for determination of the rainfall early-warning index threshold was performed, and a model for solving the rainfall early-warning index threshold was developed based on the regional critical rainfall method, the same frequency method of rainfall events and disasters, and the R/S analysis method. Then, the model was verified through its application to analysis of the rainfall time series in Taixing City, Jiangsu Province. The threshold for the maximum daily rainfall time series was determined, the its variation trend was analyzed. Results show that the threshold obtained with the model is more accurate than that of single models, and has a certain timeliness, which can provide reference for rural flood control forecast and early warning.