Infantile severe acute subdural hematomas (ASDHs) usually require a decompressive craniotomy. However, these infantile patients often suffer surgical site infection and aseptic bone-flap resorption after external decompression. In this report, we showed a case of a simplified hinge decompressive craniotomy in an infant with severe ASDH. A 2-month-old girl suffered from status epilepticus, impaired consciousness, multiple rib fractures, bilateral fundus hemorrhage, and a right ASDH. We performed a simplified hinge decompressive craniotomy, making a vascularized bone flap with a hinge using the partial temporal bone and temporal muscle and not fixing the bone flap like an inverted gull wing. Cranioplasty was performed 4 weeks after the decompression craniotomy with replaced resorbable substitute dura. Six months after the transfer, her development was generally in line with her age. The decompressive craniotomy with an inverted gull-wing hinge has shown a good outcome.