Abstract: Yaopo Formation is the important coal-bearing strata in Beijing area.The paper emphatically studies and analyzes the features of igneous rocks and pyroclastic rocks.The study results indicated that the volcano eruption offered the basement for Yaopo Formation and caused the swelling of Qiangfengpo and Hulupeng before Yaopo Formation; the pyroclastic materials fell down to the lake, made the lake lower and coal layers were formed during Yaopo Formation deposited.The magmatic intrusion destroyed the coal-bearing formation after Yaopo Formation deposited.