Instrument landing signal generator is special testing equipment for the airborne equipment of instrument landing system. At present, there is no publicly published national and industrial technical standards for verification and calibration of instrument landing signal generator in China. By analyzing the principle of instrument landing system, and starting from the working characteristics of instrument landing signal generator, this paper analyzes the signal characteristics of localizer, glide path beacon and marker beacon, gives the measurement characteristics, and presents the calibration method of each measurement characteristic based on direct measurement method of spectrum analyzer. The uncertainty of measurement introduced by spectrum analyzer is analyzed, and the extended uncertainty is evaluated by GUM method. The results show that the calibration method presented in this paper can meet the calibration requirements of the key parameters of the instrument landing signal generator, and the calibration with spectrum analyzer meets the traceability requirements of the measurement characteristics of instrument landing signal generator.