Erosion wear of the artillery barrel is divided into two primary categories: thermochemical erosion and mechanical wear. However, the majority of studies concerning this subject matter emphasize the former, and the latter has not been given enough consideration. To describe the coupling relationship of thermochemical erosion and mechanical wear, this article is inspired by the frictional behavior between the barrel and the projectile and proposes a material degradation model for thermochemical erosion considering frictional temperature rise. Under the coupling of the forced heat convection of high-temperature propellant gas and frictional heat, the friction state between the barrel and the projectile is changed from dry friction to hydrodynamic friction, resulting in a novel mechanical frictional wear model. Subsequently, numerical simulations of the thermochemical erosion and mechanical wear models are carried out. The results show that the erosion wear of the artillery barrel is divided into four regions along the axial direction: thermochemical erosion, thermochemical-mechanical erosion, transition, and mechanical wear regions. Four regions are concentrated in the interval of [0 mm, 500 mm], [500 mm, 1750 mm], [1750 mm, 4000 mm] and [4000 mm, 6800 mm], respectively.