River sediments contain important information such as hydrodynamic conditions and paleoclimate changes at the time of formation.Therefore,the study of river sediments can not only indicate the hydrodynamic conditions at the time of deposition,but also explore the paleoclimate inversion.Yixun River is located in the east section of Yanshan.The further study on the fluvial sediments in the lower reaches of Yanshan Mountains can provide some reference for the Paleoenvironmental Significance and research methods of the fluvial sediments in Yanshan Mountains.Methods:Through field investigation,optical luminescence dating,grain size analysis and magnetic susceptibility,T3 in the lower reaches of the Yixun River was studied.Results：Preliminarily established the formation time of T3 in the lower reaches of the Yixun River,which was roughly from the late Late Pleistocene to the early Holocene (13.14 ± 76 ka BP to 9.55 ka BP ± 58 ka BP),and the grain size parameters and magnetic susceptibility were discussed.It was found that the T3 front section of lower reaches of the Yixun River could be divided into 11 layers,and the grain size characteristics of each layer were obvious,but the correlation with the magnetic susceptibility parameters was not enough.Secondly,by comparing the sediment grain size of the profile with the young Dryas events recorded by various climate change indicators,it is proposed that they have a strong correlation.The YD event is well recorded in the stratification FC3,and the FC1 corresponds to the warming process in the early Holocene.Finally,guided by the grain size of sediments and the characteristics of sediments on the profile,the changes of hydrodynamic conditions in the lower reaches of the Yixun River from the late Pleistocene to the early Holocene were discussed. Finally,based on the grain size and characteristics of sediments,the changes of hydrodynamic conditions in the lower reaches of the Yixun River from late Pleistocene to early Holocene are discussed.During this period, it is determined that there are nine obvious hydrodynamic events in the lower reaches of the Yixun River,and it is suggested that the sediments in the river terraces in the lower reaches of the Yixun River have obvious response to climate change.Conclusions:Based on the sediment characteristics,formation time,grain size and magnetic susceptibility of T3 front section in the lower reaches of the Yixun River,the hydrodynamic changes in the lower reaches of the Yixun River from late Pleistocene to early Holocene and the coupling relationship with paleoclimate, especially YD events are discussed.The purpose of this study is to provide reference for the study of sedimentary history of fluvial sediments and their response to paleoenvironmental changes in Yanshan Mountains.