DAMAGE (Diffuse Axonal Multi axis General Evaluation) is an assessment criterion that quantifies the risk of diffuse injury by fitting the maximum principle strain in brain tissue using head angular acceleration. However, current understanding of the kinematic response of DAMAGE and the mechanism of DBI (Diffuse Brain Injury) in the crash test remains insufficient. By analyzing the kinematic characteristics of THOR dummy heads in vehicle MPDB crash tests, this study investigates the second-order system response characteristics of DAMAGE and identifies key factors that influence the peak magnitude of DAMAGE. Additionally, based on THUMS (Total Human Model for Safety) head model, a six-degree-of-freedom head model with prescribed motion boundaries was constructed to investigate diffuse injury characteristics and mechanism under MPDB tests. The findings indicate that high strain concentration areas tend to form in the deep frontal lobe and periventricular white matter regions, which increases the risk of DBI. Furthermore, the lower MPS calculated with THUMS than those predicted by DAMAGE was observed. This study offers new perspectives for utilizing the DAMAGE in assessing the risk of occupant head injuries and enhancing safety protection.