Abstract: The air absorbed dose rate factor of high pressure ionization chamber was calculated by Monte-Carlo method for ⁶⁰Co and ¹³⁷Cs source, and the calculated result was compared with the calibrated result in the standard reference gamma radiation field of ⁶⁰Co and ¹³⁷Cs. The relative deviation between calculated and calibrated value is 0.65% for ¹³⁷Cs reference gamma radiation, and is -5.5% for ⁶⁰Co reference gamma radiation. The results from two methods are accorded with each other in the range of uncertainty.