Objective To investigate the effect of modified decompression craniotomy (MDC) for treatment of extremely severe post-traumatic acute diffuse brain swelling (PADBS).Methods Forty-eight patients with PADBS out of which 31 underwent standard large trauma decompression craniotomy (SDC) and 17 MDC were analyzed retrospectively.Clinical data,cranial capacity compensation,postoperative complications,and Glasgow outcome scale (GOS) 6 months after operation were recorded and compared between the two groups.Results Increased cranial capacity compensatory value accounted for 8.2％ of the cranial capacity after MDC.Postoperative complications included rehemorrhage,intracranial infection,incisional hernia,epilepsy,cerebrospinal fluid leakage,and hydrocephalus and no statistical differences were observed between the two groups (P ＞ 0.05).Based on GOS,the outcome was good in 13 patients (42％),poor in 13 (42％),with 5 deaths (16％) in SDC group,while the outcome was good in 13 patients (76％),poor in 3 (18％),with 1 death (6％) in MDC group.The outcome in MDC group was better than that in SDC group (Z =2.318,P ＜ 0.05).Conclusion For patients with PADBS,MDC can improve the outcome and prognosis.