Abstract: This paper deals with the composition and distribution of loess sediments in Kereya river valley, studies the source and deposition environment of the loess.The following conclusions have been obtained：（1）the loess deposition in Holocene；（2）the main compositions are sand and salt sand；（3）deposition environment' is very dry, response to the geochemical compositions, mineral compositions, PH,CaCo₃ ect；（4）loess is transported from Takelamagan sand land；（5）distribution altitude is about 2600-4100 m.a.s.l, the higher the altitude, the thiner the loess；（6）loess formation is very weak, CaCo₃ and soluble subject keep originally.