Abstract: In order to study the internal corrosion of gas injection/withdrawal pipeline in one underground gas storage, Dry Gas Internal Corrosion Direct Assessment (DG-ICDA) method and Wet Gas Internal Corrosion Direct Assessment (WGICDA) method were applied to assess this pipeline through four steps, i.e., pre-assessment, indirect inspection, detailed examination and post assessment. In the pre-assessment step, ICDA regions are divided from two aspects of mileage and time, based on the characteristics of bidirectional flow at irregular intervals. In the indirect inspection step, WG-ICDA method is used to assess gas withdrawal process and DG-ICDA method is used to assess gas injection process. In this step, not only normal gas injection or withdrawal periods, but also longer shutdown periods are taken into consideration. In the detailed examination step, wall thickness is measured by the ultrasonic thickness gauge to determine if the pipeline is suffered from internal corrosion. And in the post assessment step, the reassessment interval of this pipeline is evaluated. The assessment results indicate that there is internal corrosion in this pipeline, but the remaining strength at the defects is not affected significantly.