Objectives: The “8·7” huge debris flow disaster in Guaza gully, Zhouqu, Gansu, has caused serious losses to local people’s lives and property. This paper focus on the correlation degree between the susceptibility index of debris flow disaster and different influencing factors that is to identify the main influencing factors, which is to provide basis for prevention of debris flow hazards. Methods: Firstly, this paper summarizes and concludes the survey data with different debris flow gullies in Guaza gullies, which combined with “8·7” large debris flow disasters instance in Zhouqu County Gansu Province. Secondly, the susceptibility value of different mudrock flow hazards gullies are calculated based on the AHP method. Finally, the influence degree of various environmental factors on the susceptibility index with the debris flow gullies is analyzed by the gray correlation method. Results: the vulnerability of debris flow disasters determined by AHP is consistent with the results of field investigation, that the AHP can be applied to the prediction of debris flow hazard. It has a significant impact on the susceptibility of mudrock flow hazards from the number of geological disasters in channel, the average slope of gully, day maximum rainfall quantity, forest cover and catchment sizes. The susceptibility of debris flow disaster is relatively close which are affected by the number of disaster and the channel slope, the maximum rainfall quantity, vegetation coverage rate and catchment sizes, gully length, beach angle and channel width. Conclusions: The method of grey relational theory has been successfully applied to analysis the correlation degree between different influencing factors and the susceptibility of debris flow disaster, providing a guiding role for the prevention and control of mud- rock flow hazards in similar areas.