When the infrared radiation of aerial object transmits through the air, it can be absorbed or scattered by the air and the aerosol in it. So the infrared radiation energy is extincted. The quantity of extinction can be described by the extinction coefficient. Extinction coefficient differs according to different wavelengths. If the weather condition of the atmosphere changes a little in short time, we can consider that the extinction coefficient has no change. Infrared detector can detect infrared radiation of different wave bands and the location of the aerial object is determined by some signal processing method. In the paper, the formula which makes use of extinction coefficient to locate the aerial object is derived and some examples are also illustrated.