A disastrous debris-flow event occurred at Aizi Ｒavine in Ningnan County, Sichuan Province between 5: 00 and 6: 00 am on June 28,  2012. As of July 4, 7 people were killed and 33 missing. The debris flows were triggered by a local intensive rainfall of 38mm/h after one month antecedent rainfall. The formation area was the subcatchment belonging to the upstream right tributary. Massive material from hill slopes and small gullies was concentrated in a short duration of approximate 30 minutes. The peak discharge was amplified by 3 to 4 times because meandering channels and narrow passes of the main stream accumulated the flows, and a great deal of debris from colluviums,  diluvium, and sediment deposit in the downstream channel were eroded. The event is characterized with short duration of formation and propagation, moderate scale but high peak discharge, and inter-occurrence of floodand debris flow. A lesson from the disaster is low-frequency  debris-flow ravines such as Aizi should be paid special attention in the hydropower engineering area.