It is of great importance to study the infrared radiation characteristics of flow over hypersonic interceptors for the design of infrared seeker. The flow field over a hypersonic interceptor was simulated numerically by solving Navier-Stokes equations with chemical non-equilibrium terms. Based on the flow field, the infrared radiation from the flow over the optical window on the side of interceptor in 0.8-20 μm range was computed using a spectral band model, and the change rules of the flow radiation versus flight parameters were researched. The research shows that the spectral radiation of the flow mainly comes from the vibration-rotation bands of CO2 and NO molecules, the change rules of spectral radiation versus flight altitude are dominated by the number densities distribution of molecules species in the flow with a constant flight Mach number, and the change rules of spectral radiation versus flight Mach number are controlled by flow temperature with a constant flight altitude, and the spectral radiation of NO molecule in the flow strengthens with increasing flight Mach number.