Abstract: In order to understand the characteristics of landslides and collapse masses transforming into debris flow, we researched the landslides and collapse masses in debris flow formation area. In this paper, we took Yuzixi river basin between Yingxiu county and Wolong county as research area and 23 debris flow gullies as research objects. Area of the study region is about 396 km², and total area of debris flow basin is about 208 km².On the basis of interpretation of the landslide and collapse points with high resolution remote sensing images, in association with field investigation, we confirmed the reliability of the remote sensing interpretation, and finally obtained 2 741 disaster points with an area of 23.6 km². Then we employed GIS to calculate the distribution of the landslides and collapse points in aspects of elevation, gradient, dip, lithology and distance from the river. Results show that, firstly, most landslides and collapse masses exist in the elevation of 1 500-3 000 m; secondly, the area ratio of landslides and the collapse masses with slope gradient of 40°-50° is the largest; thirdly, slope direction is concentrated in the range of 90°-180 °, and slope direction of the range is perpendicular to the earthquake fault; furthermore, under earthquake or heavy rainfall ,harder diorite easily leads to a large number of landslides and collapse masses; finally, landslide and collapse easily break out when mountains are near the river.

Key words: landslide, Yuzixi River, collapse, debris flow, spatial distribution characteristics