The facility and theory for measuring atmospheric spectral transmittance by solar irradiance were analyzed. An instrument system for atmospheric optical properties measurement was developed. The solar spectral irradiance was acquired by using a flat field and imaging concave grating and a linear CCD. The real time atmospheric spectral transmittance with the variable of wavelength band was obtained by employing a specific calibration method,and it can represent the molecular absorption effects on atmospheric radiation. The results were validated by comparing them with other instrument.