Abstract: Aiby Lake is a typical closed lake in inland of arid area. The changes of lake surface and hydrodynamic conditions are well recorded by grain-size characteristic of lacustrine sediments. In this research we acquired a drilling core of lacustrine sediments named Ash, and its length is about 180 cm. This drilling core is below current lake surface and near the shore. It is estimated that the sediments formed 300 aBP. 90 sedimentary samples have been taken and the distance of two adjacent samples is 2 cm or 1 cm. Granularity of the samples is measured and the fractal dimensions are calculated in this research. Based on the characteristics of grain-size dimensions, we can draw these conclusions： (1) The granularity of the sediments from the whole section is fractal, i. e. the distribution of the size of grains is statistically self-similarity. The mean value of fractal dimensions is 2.3121. The curve of fractal dimension verse depth can be clearly divided into 4 parts. Every part has different change characteristics. Compared to traditional parameters of granularity, fractal dimension can better differentiate the changes of environment. (2) Fractal dimensions of sediments from this section well indicate the modern changing process of Bortala River transporting fragments to Aiby Lake. Combined with the lithology of the drilling core, the periodical changes of fractal dimension show the fundamental changing process of the river transporting ability： from strong to weak. (3) The value of fractal dimension (D) and its correlation coefficient (R) provided by fractal research to granularity of sediments present a set of new granularity index. Combined with traditional granularity parameters, the science sense of using fractal dimension in environment research is well showed by the granularity fractal research on Ash drilling core. More research should be done to understand the accurate meaning of fractal dimension changes.