This article employs Fourier transform infrared spectroscopy to investigate radiometric calibration methods and the measurement of continuous atmospheric transmittance across the shortwave infrared band. The presence of multiple strong absorption bands within the shortwave infrared spectrum (0.9-2.2 μm) leads to significant errors in the commonly used Langley method, and even the improved Langley method struggles to yield accurate results for the calibration of these strong absorption bands. To fulfill the high-precision measurement demands for atmospheric transmittance across the entire shortwave infrared band, this paper introduces an enhanced method for calculating atmospheric transmittance. Initially, the Langley calibration technique is utilized to determine the instrument calibration value and response function K in the non-absorption band. Subsequently, the instrument response function in the absorption band is derived by interpolating the wavelength based on the instrument response function calibrated in the non-absorption band. Ultimately, the instrument calibration value is established by correlating it with the solar irradiance at the atmosphere’s top, thereby obtaining the atmospheric transmittance across the entire shortwave infrared band. Compared to results calculated by the medium-resolution atmospheric radiative transfer model software CART, the atmospheric transmittance values obtained using this method within the 0.9-2.2 μm band exhibit an average error of less than 2.5%.