Based on the analysis of the temporal and spatial distribution characteristics of the rainfall which triggered the “8.8” Zhouqu extremely big debris flow, the authors found that the rainfall has characteristics such as being heavy, short duration and obvious local variations.Based on the above, it is suggested that the characteristics of the rainfall should be fully considered in the design of comprehensive treatment projects of debris flow during post-disaster reconstruction phase.That is to take the condition when the whole Sanyanyu is covered by the same rainfall magnitude of this time as the most unfavorable extreme circumstance to calculate the maximum flow.