The “self-sharpening” effect has been observed experimentally in the penetration of tungsten high-entropy alloy (WHEA)into steel targets in previous study.From the microscopic observation of the residual WHEA long-rod projectile (LRP),the multiphase structure at micro-scale of WHEA is the key effects on self-sharpening penetration process.In order to describe the distinctive penetration behavior,the interaction between micro phases is introduced to modify the hydrodynamic penetration model.The yield strengths of WHEA phases are determined based on the solid solution strengthening methods.Combined with the elbow-streamline model,the self-sharpening mechanism is revealed in view of the multi-phase flow dynamics and the flow field in the deformation area of the LRP nose is characterized to depict the shear layer evolution and the shape of the LRP\'s nose as well as the determination of the penetration channel.The self-sharpening coefficient considering the reduction of nose radius is proposed and introduced into the penetration model to calculate the depth of penetration and the penetration channel.Results show that the multi-phase interaction at the microscopic level contributes to the inhomogeneous distribution of the WHEA phases.The shear layer evolution separates part of the LRP material from the nose and makes the nose radius decrease more quickly.It is also the reason that WHEA LRPs have a pointed nose compared with the mushroom nose of WHA heavy alloy (WHA) LRPs.The calculated results agree well with the corresponding experimental data of WHA and WHEA LRPs penetrating into semi-infinite medium carbon steel targets with elevated impact velocities.