Lake sediments were sampled from the Buha estuary of the Qinghai Lake. These samples were analyzed using a Malvern2000 Analyzer,and the parameters of grain size were obtained. Sedimentation rates were determined with radioisotope ~(137)Cs. The results suggested that the parameters of grain size varied regularly with the fluctuation of hydrodynamic conditions. The sedimentary rates of deep sediments were 0. 137 and 0. 078 cm·a~(- 1), and the mass accumulation rates were 0. 105 and 0. 030 g·cm~(- 2)·a~(- 1) in cores QH06 and QH08,respectively. Near the lakeshore,~(137)Cs flux was large,the sedimentary rate was high,and the sorting was good. Based on the analysis of the characteristics of grain size,the Buha estuary of the Qinghai Lake experienced the following three environmental evolution stages: it was dry during the period from 1853 to 1886,humid from 1886 to 1940,and dry again from 1940 to 2013,respectively. Significant changes of grain size in 1978 and 1989 corresponded with the hydrological data,they also revealed that grain size could be regarded as a reliable indicator of climate change. The environment change at the estuary may be related to human activities.