Abstract: Through the analysis on the sensitivity of short-wave infrared(SWIR) detectors, the signal-to-noise ratio(SNR) of the target and the environmental detection output and the contrast, the detecting distances of SWIR thermal image to external scenes and laser spots under different atmospheric visibility and ambient illumination conditions were calculated and theoretically analyzed, moreover, the theoretical analysis was verified by testing.The results show that the detection distance of the laser spot by the SWIR thermal image is less than 3.5 km in the conditions of atmospheric visibility 1 km~3 km, ambient illumination 1 lx~1 000 lx, threshold SNR 2.25~10, and threshold contrast ratio 0.01~0.02.