In August 2009, Typhoon Morakot raided Taiwan, including heavy rain in southern Taiwan. Stones from large-scale landslides blocked river bed and forming many landslide dams. According to field investigation and satellite imagery analysis, a total of 16 landslide dams were formed as a result of Typhoon Morakot's passing and 7 still exist at present. Because landslide dams are characterized by differences in formation, rainfall, and spatial distribution, it shows that the high rainfall intensity, long storm duration, and large areas by Typhoon Morakot not only to induce landslide dams but also influence its formation and collapse styles. Base on the investigation, this study categorized the Typhoon Morakot landslide dams by means of following conditions:(A) not collapsed, (B) partially collapsed, but still exists and (C) collapsed and no longer exists. It is easy to form many landslide dams in the same mainstream due to the natural dams contain high water content and low coefficient of permeability. Besides, the upstream flow come fast and big, so that the timing of storage is relatively short and easy to induce partially break or broke. When many landslide dams formed in one mainstream that cause continuous dams collapse. When the most upstream landslide dam collapses, the peak flow it brings impacts the next one, and the next one combined with the first impact that will produce a bigger peak flow. That is why the downstream landslide dams exit only for a short period of time.