In order to solve the problem that the reference radiation field should be provided for field calibration of fixed radiation dose rate monitoring instruments used for on?site online monitoring, this work developed a portable radiation source irradiation device based on γ source using Monte Carlo simulation method. The radiation source shielding switch gears are not less than 3, the surface leakage ray is lower than 0.5% compared with the useful ray beam, and the radiation field non?uniformity is less than 5%, which meet the fixed X or γ radiation dose meter field calibration needs. The study has improved the quantity transfer ability for the field calibration of the fixed dose rate meters.