Infrared optical system self-thermal radiation was evaluated, calculated and measured. Firstly, it introduced and compared the two kinds of the thermal radiation way of evaluation, effective emissivity and equivalent blackbody radiation temperature; Secondly, the way based on experiment of calculation for equivalent blackbody radiation temperature of self-thermal radiation was introduced in detail; Finally, the coaxial reflection infrared optical system thermal radiation was measured by using self-thermal radiation test platform and error analysis was carried out. The result show that self-thermal radiant exitance is proportional to the square of effectively F number of optical system and the linear coefficient for the output gray of self-thermal radiation between the integral time, is inversely proportional to transmittance. It shows that the equivalent blackbody radiation temperature for self-thermal radiation of coaxial reflection infrared optical system is 217.3 K. Error for radiation form background simulation board is 8.5%, the relative uncertainty of linear coefficient for the output gray of self-thermal radiation between integral time is 0.2%. It shows that infrared detector has a good stability under 5×10-4 Pa.