Abstract: A pancake ionization chamber made by graphite, with volume of 6.981 6 cm³, was fabricated to absolutely measure the air kerma for ⁶⁰Co gamma ray. The current acquisition system was used to collect the current signals of the ionization chamber in the field of 50 TBq ⁶⁰Co gamma ray irradiator of the National Institute of Metrology. The physical parameters and the correction items were obtained by experiment measurement or Monte Carlo simulation. The combined standard uncertainty of the device to measure the air kerma for ⁶⁰Co gamma ray is 0.24%. A comparison between the pancake ionization chamber system and the spherical-cylindrical ionization chamber primary standards for air kerma was made. The comparison results expressed as a ratio of ⁶⁰Co gamma ray air kerma, with value of 0.998 7, is accordant with the combined standard uncertainty of 0.23%.