This paper describes a new method for determining the amount of earthquake-added soil erosion in Wenchuan earthquake area. To study on the method, typical landslides were chosen in Wenchuan County, and the information of typical landslide surface and its surrounding terrain were obtained by on-site measurement. The rill/gulley on the landslides were identified by image analysis, and the amounts of slope erosion from landslides were estimated by numerical calculation. The on-site measurement was carried out by using a 3-D laser scanner (HDS3000, Leica Company). The scanning distance reached as far as 300m, with a distance measurement accuracy of ±4mm at 50m. The scanner was set up in front of the slope of the landslide to be measured. The distances from the scanner to near end and the far end of the landslide were 58.32m and 136.81m respectively. The scan grid was set to 20.0cm horizontal and 20.0cm vertical at 200 m from the scanner. The actual scan grid of the measured landslide was 5.8cm×5.8cm at the near end and 13.7cm×13.7cm at the far end, respectively. Landslides surfaces sections prior to erosion were specified by using least squares curve fitting method, and fitting it with curve of the second degree. The gully volume was estimated by comparing the result of surfaces prior to erosion and on-site data collected with laser scanner. The erosion volume of a typical landslide surface gully from 2008 to 2012 was estimated to be 355m3. The method was verified with the data calculated by traditional cross section area method. The cross sections area and length of gully were calculated by the built in method of the 3-D laser scanner. The result showed that the values calculated by the method suggested were a little bigger than that by the traditional cross section area method. The relative error of the method was 15.6% for the whole gully, with the lowest being 7.9% and the highest being 27.1% for the segmentations. The reasonable accuracy of the method showed that the rill/gully volume of landslide could be estimated reliably by using it in engineering application.