With the continuous progress of science and technology, military targets are developing towards miniaturization, ultra-high speed and low detectivity, so the detection and identification ability of targets is also put forward higher requirements. Based on the deep analysis of point target imaging process and on the basis of energy distribution, based on abnormal Rayleigh distribution of point target energy calculation method, the infrared radiation characteristics and has a better precision than the experimental verification, it is concluded that the measurement deviation of radiation intensity can be controlled under 8%, and measuring the degree of discrete numerical smaller, can effectively distinguish between the point target and background. It is proved that the calculation method has good engineering applicability, high measurement accuracy and wide application prospect.