Tunnel boring machines (TBMs) are widely used in tunneling engineering. Due to the harsh and complex working conditions, the TBM disc cutters suffer extensive wear, resulting in large economic losses. Among many influencing factors, the contact angle between the rock and the cutter significantly influences the cutter ring. In this study, the composite wear properties of the cutter base material (H13 die steel) were investigated at different impact-sliding angles to determine the wear mechanism. The results show that the damage to the impact region of a flat sample is primarily caused by the large contact stress generated by the high-strength instantaneous impact. The damage is positively correlated with the impact-sliding angle. As the contact angle increases, the contact duration during the sliding process increases, and the area of the flat sample with the most damage changes from the impact region to the start of the sliding region. In addition, the wear mechanism of the flat sample changes from abrasive wear to mixed abrasive and adhesive-fatigue wear. This work is a fundamental study of the microscopic wear mechanism of the H13 steel, which is used in the TBM cutter. Therefore, the results reflect the wear conditions of the TBM cutter at different contact angles and provide significant guidance for the installation of the TBM cutter.