The theory of human body infrared radiation indoors plays an important role in the fields of infrared detecting,disease diagnostics,medical treatment,scout and rescuing work after disaster occurring. Presently,the systematic and comprehensive model for detecting infrared radiation of human body indoors has not been studied. To improve the detecting and recognizing abilities of infrared system,a method of calculating the temperature field and the radiant flux intensity of human body is proposed to build the detection model by using infrared physics and heat transfer theory on the basis of bio-heat equation. The temperature field of human body in indoor environment is systematically discussed according to the physical structure and thermoregulation system. The main factors influencing body temperature are analyzed. The experimental results indicated that the main theoretical value is within the error range.