Abstract：The Inggen-Ejin Qi basin, Inner Mongolia, is a Meso-Cenozoic continental basin, and pre-Mesozoic rocks constitute its basement. It entered the stage of downfaulted basin development in the Late Triassic-Jurassic and the stage of complete development in the Early Cretaceous. The Late Cretaceous was a subsidence stage and later the basin was in a state of compression and uplift. In the basin there were developed a Mid-Lower Jurassic petroleum-bearing system and a Lower Cretaceous petroleum-bearing system, and some subbasins have superior source, reservoir and seal conditions and combinations. Exploration practice has confirmed that there occurred hydrocarbon migration and accumulation, showing that the basin has good petroleum prospects. At present it is necessary to grasp the key exploration targets and, proceeding from favorable areas (zones) and traps, pay attention to the characteristics of the lacustrine sedimentary evolution and influences of magmatic rocks on the evolution of source rocks and petroleum accumulation. Only in this way, can a breakthrough in petroleum exploration be made and will a new situation of petroleum exploration be opened in the area.