The shock layer of high-speed missiles is composed of gas medium with highly uneven temperature distribution. A model for the radiative heat transfer in this layer was developed. With the method of discrete transfer and the model of light transmission, the heat radiation strength of the shock layer was calculated by the line of sight along the seeker detectors. The relations between the shock wave thermal radiation noise and flow parameters were also analyzed and the empirical formula is given. The results showed that for 3~8 μm infrared band, the thermal radiation noise and the Mach number is closely related. The radiation alters very little with the change of flight height (in atmosphere).