Objective To investigate the equivalent conversion of head injury criterion (HIC) under anterior-posterior (AP) and lateral-medial (LM) craniocerebral impact for mild craniocerebral injury in rats using motor evoked potential (MEP) and β-amyloid precursor protein (β-APP) immunohistochemistry (IHC). Methods Sixty healthy adult male SD rats were randomly divided into 0 m control group, 0.5 m-AP and 0.5 m-LM injury groups, and 1 m-AP and 1 m-LM injury groups (12 rats in each group). The control group did not undergo any impact injury experiment. After the impact injury experiment, the injury and control groups were subjected to excessive anesthesia to produce β-APP immunohistochemical stained slices, and the percentage of positive area and integral optical density (IOD) in the brainstem pyramidal tract area of the slices were determined. The MEP groups were divided in the same manner as the IHC groups and the MEP amplitudes of the MEP and control groups were measured after the impact injury experiment. Results With an increase in the degree of injury, the decrease in MEP amplitude, percentage of positive areas, and IOD in the injury groups significantly increased. When the degree of injury was low, the sensitivity of IHC was higher than that of MEP. When the degree of injury was the same, the HIC in the LM direction was lower than that in the AP direction. When the HIC was the same, the degree of injury in the LM direction was greater than that in the AP direction. Conclusions The joint evaluation of MEP and β-APP can provide experimental references for the study of HIC equivalent conversion in AP-LM craniocerebral impact injury.