Diabetic ketoacidosis (DKA), a serious acute complication of diabetes mellitus, mainly manifests as hyperglycemia, ketosis, and acidosis. It is a metabolic syndrome resulting from insulin deficiency and increased insulin-antagonistic hormone levels. While type 2 diabetes mellitus complicated by DKA is relatively uncommon, secondary pneumomediastinum in DKA is extremely rare. Following alveolar rupture, air can travel through various routes to reach the hilum, causing anterior, middle, or posterior pneumomediastinum or even leading to intracranial epidural pneumatosis. The diagnosis of pneumomediastinum is mainly dependent on chest computed tomography findings. After the successful treatment of DKA, pneumomediastinum usually resolves spontaneously within 5-10 days with a good prognosis. One DKA patient admitted to Dege County People's Hospital developed Kussmaul respirations, followed by an increase in intra-alveolar pressure, an elevation in intra and extra-alveolar pressure difference, and protein decomposition in the alveolus wall, which promoted alveolar rupture and induced mediastinal emphysema. After rapid fluid replacement, blood glucose control with insulin, and maintenance of acid-base balance (correction DKA), the mediastinal emphysema was spontaneously absorbed. Through the analysis of the clinical data of this case, the purpose is to improve the clinicians' internal understanding of the relationship between mediastinal emphysema and DKA, avoid over-examination and over-treatment, and provide strategies for correct diagnosis and treatment.