Overdischarge is one of the main factors of lithium-ion battery failure, due to the inconsistency of lithium-ion battery in pack. However, the failure mechanism remains unclear. This article introduces the X-ray computed tomography (CT) to explore the gas production and copper dissolution of lithium battery during overdischarge state. From tomographic images in two different cross-sectional directions, the internal structure changes of bulge deformation and copper deposition are observed to quantitatively analyze the relationship between copper deposition and overdischarge state of charge. The position distribution is analyzed by density distribution feature, which indicate that the gas production is mainly distributed in the middle of the battery, and the copper deposition is distributed around the outer side. The experimental result shows that X-ray CT is a nondestructive, quantitative, visual, and effective way to study the internal structure and material distribution of the overdischarge battery, so as to effectively monitor the state of the lithium-ion battery, to avoid dangerous problems such as internal short circuits and thermal runaway.