In order to improve the sampling accuracy of bed materials, we carry out a contrast test in siltation observation of Xuwei test channel among three methods including sampling by dragging dustpan,sampling by thin-walled drill pipe dragging and sampling by thick wall. Based on the comparison and analysis of the field and lab results, we propose the improved sampling method for bed materials with thick wall, which can not only raise the sampling efficiency greatly but also reduce the labor intensity under the prerequisite of satisfying the sampling requirement. The method is widely used in the siltation sampling of the region.