Abstract: The grade of oil and gas shows in exploratory wells in the south slop of Tazhong uplift is low and the abundance index of source rock in the parameter well Tang - 1 cannot reflect the hydrocarbon generation potential in this depression, therefore oil sources are the unsolved problems that impeding exploration in this area. The lower limit of organic carbon in marine carbonate is set at 0. 3% according to regional evolution of source rock in Tarim basin and the relationship between sedimentary facies and organic abundance. It is believed that there exist two sets of source rocks of high quality in Tazhong uplift and the neighboring Tanggubazi depression including the Cambrian - Lower Ordovician and the Middle and Upper Ordovi-cian. The former belongs to medium- good source rock, while the latter has an averaged organic carbon ranging from 0. 500% to 0. 947% and belongs to medium or better source rock.