We investigate the change of the default mode network (DMN) by using amplitude of low-frequency fluctuation (ALFF) and functional connectivity (FC) methods in acute phase patients after severe traumatic brain injury (sTBI) and correlate these changes with prognosis. Twenty-one patients with sTBI were included. Twenty-one healthy sex-, age-, and education-matched control subjects were recruited for the control group. Of the 21 patients with sTBI, 12 patients regained consciousness (Glasgow Outcome Scale [GOS] score >2) and 9 patients remained unconscious (GOS score <2). FC and ALFF values were measured in the DMN and compared between the groups. We further assessed and compared the FC and ALFF values in both groups. Patients with sTBI showed significantly decreased FC and ALFF values in the DMN. However, patients with a better prognosis showed a significant increase in FC and ALFF values in the DMN. The conscious subgroup showed significantly enhanced FC in the medial superior frontal gyrus, left temporal gyrus, anterior cingulate gyrus, precuneus, posterior cingulate gyrus, and parietal cortex compared with the coma subgroup. Increased ALFF values in the right frontal gyrus, right temporal gyrus, and right inferior parietal gyrus were significant in the conscious subgroup compared with the coma subgroup. Increases in FC and ALFF values in the DMN are related to better prognosis in patients with sTBI. Copyright © 2018 Elsevier Inc. All rights reserved.