At about 8 o'clock on April 9th 2000, a large rock fall - landslide occurred near Yi'ong, southeastern Tibet. Topographically, this region lies in a transitional zone from the highs of the Tibetan plateau to the lower mountain areas, where the gravity effect dominates the surface geological process. Tectonically, Yi'ong is located to the west of Assam where the India plate wedges into the Eurasia plate. Field investigation with the GPS 12XL combined with the analysis of satellite images taken before and after the landslide revealed that the deposits of the landslide formed a "dam" that is 5. 7 km long and 1. 5 km wide, which entirely blocked the Yi'ong River. The volume of the deposits is more than 3. 8X 10s m3. According to the recordings of the local seismic network, the landslide occurred at 19:59:18. 2 local time and the duration of the vibration is about 6 minutes. Three seismic phases were identified from the seismogram, which represent three large surface vibrations. The speed of the debris flow is about 48 m/s and that of the mud flow is about 16 m/s, which is much larger than a normal mudflow.