Traditional zooarchaeological and archaeobotanical methods based on morphological identification of the excavated faunal and floral remains have been broadly used in reconstructing ancient subsistence economies. However, the accuracy and reliability of these methods rely heavily on the preservation state of the remains. By sequencing the ancient DNA of plants, animals, and microorganisms preserved in sediment, sedimentary ancient DNA (sedaDNA) now offers a novel approach for reconstructing the taxa composition dated back to hundreds of thousands of years. Yet, its application in open-air archaeological sites is rarely reported. In this study, we attempted to apply sedaDNA shotgun metagenomics on the archaeological deposits of the Khog Gzung site (an open-air site dated to 3160–2954 cal yr BP) on the Tibetan Plateau, and then compared the reconstructed taxonomic composition to the unearthed remains. Results showed that most of the crops and domestic animals identified by the two approaches, such as barley (Hordeum vulgare) and sheep (Ovis aries), are in general consistent. Some species, such as foxtail millet (Setaria italica), however, was only detected by sedaDNA. In addition, a variety of microorganisms were also detected by the sedaDNA. The two approaches combined revealed diversified food recourses at the Khog Gzung site, which included crops such as millet, barley and wheat, domestic animals such as sheep and cattle, and likely also wild animals from fishing and hunting. Our data proves that sedaDNA has a great potential in reconstructing the faunal and floral compositions from archaeological deposits, therefore laying the foundation for its border applications.