Image method, as the grainsize analysis method recommended only by the International Union of Geological Sciences, has long been constrained by insufficiency of sample capacity. The new dynamic image method, based on the new imaging and processing technology, can set up the database of mass grainsize in short time, and opens up broad prospects for direct expression of grainsize of natural sediment. In this study, the sediments of alluvial fan alone the bank of the Qiaojia segment, upper Yangtze River, are investigated. A total of 20 samples are collected from 4 profiles and are studied using methods of dynamic image and laser-diffraction. Based on dynamic image database of the samples, six type of grainsizes are calculated, including diameter of a circle of equal projection area, three kinds of Feret diameters (the max, min and mean), and two kinds of minimum external rectangular diameters (max and min). The results are also compared with those obtained by laser method. The study shows: (1) the median and mean grainsizes obtained by dynamic image method are coarser than those by laser method, and the sorting degree is better than that by laser method. (2) The comparison of the results normalized by sama measurement range shows the mean diameter measured by laser method is only 3/10~1/2 of the true mean diameter (the result by dynamic image method) (the difference is 0.68~1.78 φ), this deviation may be related to the multimineral properties of natural sediments. (3) The results obtained by the two methods can reflect similar trend of grainsize change in the profile, and can reflect the similar dynamic conditions and sedimentary environment under the traditional discrimination criteria of sedimentary environment. These knowledges provide technical support and explanation basis for the application and popularization of dynamic- image grainsize analysis.