To research on the combustion characteristic of polyethylene in high-speed ramjet kinetic energy projectile, the numerical simulation investigation on the integrated flow field of high-speed ramjet kinetic energy projectile was carried out. The difference of flow characteristics when ramjet working or no working was analyzed. Both the combustion and propulsive performance characteristics of polyethylene when ramjet working were analyzed. The results show that when the ramjet is working, the pressure in combustion chamber is uniform and the average pressure of the central axis is about 2.1 MPa. With increasing the axial distance x, the flame front closes to solid fuel surface at first, and then gradually keeps away from solid fuel surface. With increasing the axial distance x, both the surface temperature and regression rate of solid fuel continue to increase before re-attachment point, the maximum value is reached at the re-attachment point and then decrease. Under the aerodynamic configuration designed in this study, the nominal thrust, net thrust and specific impulse based on fuel produced by high-speed ramjet kinetic energy projectile are 250 N, 76 N and 10593 m·s^-1, respectively.