Abstract: The southern sag in Yanqi basin, a secondary structural unit in the southern part of Bohu depression, has certain exploration potentials, with Jurassic as its major exploration target. Based on analysis of heavy minerals, detrital components of gravel - bearing coarse fragments, maturity of minerals and clay components of mudstones, it is believed that Jurassic would have sourced mainly from two directions, which are the southern Kuluke Mountain and the western Tashidian area respectively.