Abstract: Caprock structure in the Songliao Basin is composed of the upper depression layers and the lower fault-depression layers.The Changling Fault-Depression(part of the fault-depression layers) is a deep-large fault-depression controlled by the Sunwu-Shuangliao and the Songhuajang-Siping Deep Fault Belts generated during basin early phase.Deep faults in and around the fault-depression cut deep into lithosphere,causing volcanic activities,resulting in association of volcanic rocks and lacustrine facies sedimentary rocks.Volcanic rocks are mainly acid,and can be divided into 2 types: explosive and outpouring.The 2 facies alternate and compose multiple volcanic activity cycles.Primary vesicles gene-rate in the upper subfacies of the explosive facies.Pores and caverns generate in the aerial-falling and thermodynamic wave subfacies of the outpouring facies.Good reservoirs generate controlled by the upper subfacies of the explosive facies and the aerial-falling and thermodynamic wave subfacies of the outpouring facies;hence control gas accumulation formation.