Abstract: With the rapid development of nuclear technology applications, the demand for medium- to high-energy X-rays has been increasing substantially, accompanied by urgent requirements for absolute measurement capabilities and measurement ranges of air kerma rates under narrow-spectrum (60-350) kV conditions. This study systematically calculates and analyzes the correction factors and associated uncertainties required for absolute air kerma measurements of N-60～N-350 standard radiation qualities using the medium-energy free-air ionization chamber established at the China Institute of Atomic Energy. The investigation employs a comprehensive methodology integrating experimental measurements, theoretical calculations, and Monte Carlo simulations. Through this research, the reproduction of air kerma values for N-series X-ray standard radiation qualities has been successfully achieved, yielding air kerma rate values at 1 meter from the focal spot under N-60～N-350 radiation qualities. Subsequently, uncertainty evaluation using the GUM method demonstrates that the relative standard uncertainty of the reproduced quantity values reaches 0.52%. Furthermore, preliminary verification of measurement accuracy has been conducted through calibration factor comparisons, thereby validating the reliability of the reproduced quantity values.