Abstract: Taking the clastic rocks of the early Triassic Longwuhe Formation in Lintan area, West Qinling orogenic belt, as the research object, the LA-ICP-MS zircon U-Pb geochronology was carried out to explore its formation age and source, and to infer its sedimentary environment. The ages of the obtained detrital zircon can be divided into 4 groups:259-418 Ma(16.8%),448-474 Ma(2.9%),848-1 115 Ma(2.9%)and 1 701-2 672 Ma(77.4%). The minimum age is 259 Ma, indicating that the sedimentary age of the Longwuhe Formation is not earlier than the Late Permian. The comprehensive regional data define the sedimentary age of the Longwuhe Formation as early Triassic. Sediment source is generally from Neo-archean-Paleoproterozoic volcanic basement in the northern side of the Longwuhe basin, including the North China Plate, the northern margin of the Western Qinling orogenic belt, and the eastern section of the Qilian orogenic belt. Combined with geochemical and sedimentary facies characteristics, it is concluded that the main body of the Longwuhe Formation sandstone formed in the active continental margin. The prototype of the basin should be the post-arc rift basin in the expansion stage.