Infrared sensitivity testing technology is used to quantitatively detect the operating distance of airborne electro-optical targeting system.In order to test and evaluate the ability of the multispectral electro-optical detecting system for searching and tracking infrared targets in middle/long distance under infield condition, an optical measurement system is designed for simulating infrared target heat source and outputting infrared irradiance quantitatively.The blackbody cavity structure and heating power are calculated according to the blackbody classic emission theory.Cassegrain-type reflection system is used to collimate and converge the optical structure to the infrared light path.The parameter relationship between the target infrared radiation characteristics and the diaphragm apertures is established, thus to test and evaluate such performance parameters as operating distance, detection sensitivity and tracking sensitivity of the electro-optical system quantitatively.The test results show that, the optical measurement system can effectively simulate the infrared target at a distance of 5～100 km, accurately calibrate the aperture diameters corresponding to 6 sets of simulated operating distances, and stably output the infrared irradiance in the response band of the electro-optical system.The infrared sensitivity test of airborne electro-optical targeting system is realized.