Type 2 diabetes mellitus (T2DM) is a risk factor for cognitive impairment. While its mechanism remains to be explored. In this study, using Automating Fiber-Tract Quantification (AFQ) analysis, we found that the fractional anisotropy (FA) in callosum forceps minor decreased in patients with T2DM, which indicated transverse white matter tracts connecting bilateral frontal cortex, was damaged. Meanwhile, functional connectivity between multiple brain regions within bilateral frontal cortex was decreased. The changes in the tract of callosum forceps minor might be the microstructural basis for functional changes of frontal cortex and help us understand the mechanism of T2DM related cognition decline.