The sub-pixel fire point is the radiation interference source of the infrared early warning satellite (IEWS). Based on the derivation of the radiation intensity equation of the fire pixel, the radiation intensity of fire point pixels in the 2.55-2.85 .m and 4.19-4.48 .m wavebands under different conditions are numerically calculated, and the factors affecting the radiation characteristics of the fire pixel are analyzed. We compared and analyzed the radiation characteristics of the tail flame of the Titan IIIB rocket andverifiedthe actual fire data. The results showed that the sub-pixel fire points in 2.55-2.85 .m and 4.19-4.48 .m wavebands can cause radiant interference to IEWS. Moreover, the radiation characteristics of the rocket tail flames were dif-ferent in that most fire pixels showed stronger radiation intensities in the 4.19-4.48 .m waveband. The re-sults can provide theoretical support for improving the ability of IEWS to resist the interference of fire-point radiation.