In order to explore the source and sedimentary environment of lacustrine sediments in the middle and upper reaches of Salawusu River Valley， the ages of three dating samples and the contents of chemical elements in 113 samples were measured， the origin of sediments reflected by the geochemical characteristics of Gangouzi section was analyzed， and the changes of sedimentary environment since Holocene was discussed. The results show that the contents of CaO， MgO， Sr， Cl and Br change dramatically with the boundary of 110 cm in the vertical direction of the section， showing obvious low value at 250-110 cm， and obvious high value at 110-0 cm. The change of provenance is the main reason for the significant increase of CaO， MgO， Sr， Cl， Br at the depth of 110-0 cm： The paleo-lake in the 12-6.7 Cal.ka B.P. （250-110 cm） was a relatively closed environment， and its provenance was mainly influenced by the source of surrounding dunes； in the 6.7-2.2 Cal. ka B.P. （110-0 cm）， the lake changed into a semi-closed environment， the river （upper reaches of the Salawusu River of today） rises in Baiyu Mountain（in the northern Loess Plateau） and into the south of the lake， its material source is profoundly influenced by the material of the loess brought in by the river.