Identification of rainfall thresholds is crucial for debris flow forecasting and hazards mitigation. The data of 34 earthquake debris flow events and their responding rainfall processes in a typical debris flow prone region (the zone along the DujiangyanWenchuan National Highway) were collected through field investigations, interviews, and literature researches, etc. The 〖WTBX〗I〖WTBZ〗〖WTBX〗D 〖WTBZ〗relationship is established by analysis of the rainfall duration and mean rainfall intensity. A new debris flow warning classification is proposed based on the rainfall division method of the meteorological department of China and the rainfall duration of the debris flows. The rainfall events are divided into three levels: smallscale rainfall (SI), mediumlevel rainfall (MI), and largelevel rainfall (LI), and the 〖WTBX〗ID〖WTBZ〗 thresholds are improved. The results indicate: (1) The rainfall duration ranged from 2 to 53 hours; the mean rainfall intensity was in the range of 0.1 to 13.8 mm/h; and the 〖WTBX〗ID〖WTBZ〗 relationship can be expressed as 〖WTBX〗I〖WTBZ〗=5.94〖WTBX〗D〖WTBZ〗0.70. (2) The compounding〖WTBX〗 ID〖WTBZ〗 prediction model can be used for hierarchical warning, and about 80% debris flow events exceed the orange warning line, which can be expressed as 〖WTBX〗I〖WTBZ〗=10.0〖WTBX〗D〖WTBZ〗-0.56 （1 h ≤〖WTBX〗 D〖WTBZ〗 < 12 h） and 〖WTBX〗I〖WTBZ〗=4.8〖WTBX〗D〖WTBZ〗-0.26 （〖WTBX〗D〖WTBZ〗≥12 h）. (3) The improved compounding 〖WTBX〗ID〖WTBZ〗 relationship has a smaller slope and higher accuracy, and more suitable for the debris flow forecasting in the mountainous areas of the western China. The results are tested by the debris flows in the period of 2014 to 2016, which shows an acceptable accuracy. This study is intended to improve debris flow forecasting and hazards mitigation for earthquakeprone regions.