Objective To explore the white matter microstructural abnormalities in patients with different subtypes of attention-deficit/hyperactivity disorder (ADHD) and establish a diagnostic classification model. Methods Patients with ADHD admitted to West China Hospital of Sichuan University between January 2019 and September 2021 and healthy controls recruited through advertisement were prospectively selected. All participants underwent diffusion tensor imaging scanning. The whole brain voxel-based analysis was used to compare the diffusion parameter maps of fractional anisotropy (FA) among patients with combined subtype of ADHD (ADHD-C), patients with inattentive subtype of ADHD (ADHD-I) and healthy controls. The support vector machine classifier and feature selection method were used to construct the individual ADHD diagnostic classification model and efficiency was evaluated between each two groups of the ADHD patients and healthy controls. Results A total of 26 ADHD-C patients, 24 ADHD-I patients and 26 healthy controls were included. The three groups showed significant differences in FA values in the bilateral sagittal stratum of temporal lobe (ADHD-C<ADHD-I<healthy controls) and the isthmus of corpus callosum (ADHD-C>ADHD-I>healthy controls) (P<0.005). The direct comparison between the two subtypes of ADHD showed that ADHD-C had higher FA than ADHD-I in the right middle frontal gyrus. The classification model differentiating ADHD-C and ADHD-I showed the highest efficiency, with a total accuracy of 76.0%, sensitivity of 88.5%, and specificity of 70.8%. Conclusions There is both commonality and heterogeneity in white matter microstructural alterations in the two subtypes of patients with ADHD. The white matter damage of the sagittal stratum of temporal lobe and the corpus callosum may be the intrinsic pathophysiological basis of ADHD, while the anomalies of frontal brain region may be the differential point between different subtypes of patients.