Abstract: By using high-resolution laser grain size instrument Mastersizer 2000,the multimodal characteristics of grain size distribution of sediments from the Angulinao Lake（41°18′～41°24′N,114°20′～114°27′E）,Santai River（41°18′N,114°24′E）,Changjiang River（32°07′N,118°46′E）,etc.are measured and carefully analyzed.The standard patterns and their grain size characteristics of various sediments are systemically summarized,the discrepancies of multimodal distribution among lake sediments are concluded and the physical mechanisms of grain size multimodal distribution are also discussed in the paper.Major conclusions include:（1） The multimodal characteristic of grain size distribution is a common feature in all lake sediments and is resulted from properties of transportation medium,dynamic intensity,transportation manner and other factors;（2） There are 6 modes（median size are 700μm,respectively）in grain size distribution of lake sediments.The former 4 are suspending while the others are saltated and rolling;（3） Lake sediments can be divided into three facies: lake shore facies,transitional facies,and central lake facies.The grain size distributions of the three facies are distinctly different with clear-cut boundaries.In all modes,the third is a criteria to identify windblown deposition in watershed.In lake shore sediments,suspending particles are dominant,a saltation mode sometimes occurs and the fourth mode is the most important one.In the transitional facies,the percentage of the fourth mode decreases and that of the second mode increases from lake shore to central lake.In the central lake facies,the second mode is dominant.A higher content of the second mode indicates its position more close to the central lake;（4） The formation mechanism of grain size distribution in lake is believed to be caused by comber in lake shore and waves in central lake.