For tracking and recognizing a flying rocket, potassium 766.490 nm and 769.896 nm in rocket plume radiation spectrum were studied by the spatial heterodyne spectroscopy. The atmospheric molecular absorption and atmospheric scattering were considered in the atmospheric transmission model. In 763-773 nm, oxygen absorption coefficient was calculated by using line-by-line method, and atmospheric scattering coefficient was calculated by Rayleigh scattering formula and the relationship between scattering coefficient and meteorological visibility. Transmittance was calculated based on Lambert-Beer law. The analyses of solar radiation spectrum and atmospheric transmittance show that these two characteristics of potassium lines in the location which solar radiation intensity is weak and high transmission efficiency, and theoretically verify the feasibility of detection of potassium spectrum. Then, the spatial heterodyne spectrometer was used to detect potassium spectrum that K2SO4 was burned in flames. The experimental datum are accordant with the theoretical results, which demonstrate that the potassium line detection scheme is feasibleusing spatial heterodyne spectrometer.