Abstract: In order to explore the relationship between the macro deformation behavior of W₂₅Fe₂₅Ni₂₅Mo₂₅ high-entropy alloy projectile and the micro structure of the material in the penetration, a two-phase flow evolution model of constant cross-section straight pipe is established. The model takes the differences of soft and hard phase density, velocity and concentration into consideration based on the simplification of the two-phase flow model. By analogy with the inflow and outflow characteristics of the materials at the head of the projectile in the macro state, the analysis area is selected. The inflow and outflow relationship of the materials in the analysis area under the two-phase microstructure is established. Combined with the microstructure evolution equation, the concentration evolution results in the analysis area are given. The flow stability coefficient t/l_length characterizing the concentration evolution rate of the materials is proposed. In order to compare the penetration behavior of projectiles with different microstructures, the typical two-phase material tungsten- copper alloy (W₇₀Cu₃₀) was selected to carry out the penetration test of two kinds of projectiles into semi-infinite steel target based on small caliber ballistic gun. The microstructure evolution behavior of the two kinds of alloy projectiles is analyzed. The results show that the distribution of hard phase concentration generally reflects the characteristics of "concentrated in the center and sparse at the edge". The higher the concentration of the hard phase, the higher the density and the faster the driving speed, the smaller the flow stability coefficient t/l_length. The better the flow stability of the projectile in the penetration, and the easier it is for the projectile head material to form a continuous plastic flow zone. The two-phase flow evolution model of constant cross-section straight pipe can be used to describe the flow stability of projectile head material in the process of penetration, and reveal the correlation mechanism between projectile head deformation and two-phase microstructure in the process of penetration.