Abstract: Stratigraphic characteristics and sedimentary environments of the Devonian Tarbaget Formation are described on the basis of regional geological survey and measurements of the studied sections in the Arxan region,Inner Mongol.The Tarbaget Formation is considered as a succession of siliciclastic sandstones intercalated with pyroclastic deposits.The sedimentary facies dominantly consist of the littoral facies.The sedimentary environments show a long and complex history,with early marine facies,marine-continental transitional facies and continental facies,and late continental pyroclastic deposits.On the whole,the Tarbaget Formation is built up of a succession of nonbarrier littoral to shallow marine shelf deposits.