<p>32CrNi3MoVE is the primary material used in gun barrels, but it undergoes significant surface degradation during artillery firing. To investigate the surface layer evolution and damage mechanisms of gun steel, controlled erosion experiments were conducted under simulated ballistic conditions. The results indicate that the surface forms a white layer under the thermochemical action of propellant gas, which is classified into inner and outer layers based on the extent of corrosion. The outer white layer, primarily affected by corrosion, exhibits a multilayered stacked structure. It is very thin (5.1 μm), has low hardness (1.15 GPa), and is rich in carbon, oxygen, and sulfur. The inner white layer experiences slight impurity infiltration and is mainly affected by thermal effects, undergoing martensitic transformation. High pressure markedly increases the concentration of reactants in the gas, accelerating surface corrosion and transforming the outer white layer into a bilayer structure. The inner white layer structure is absent due to the short duration of high-temperature exposure. Increasing the temperature, pressure, and duration of erosion can enhance corrosion, leading to a thicker outer white layer and encouraging surface delamination.</p>