The parallel-plate free-air ionization chamber termed FAC-IR-۳۰۰ was designed at the Atomic Energy Organization of Iran, AEOI. This chamber is used for low and medium X-ray dosimetry on the primary standard level. In order to evaluate the air-kerma, some correction factors such as electron-loss correction factor (ke) and photon scattering correction factor (ksc) are needed. ke factor corrects the charge loss from the collecting volume and ksc factor corrects the scattering of photons into collecting volume. In this work ke and ksc were estimated by Monte Carlo simulation. These correction factors are calculated for mono-energy photon. As a result of the simulation data, the ke and ksc values for FAC-IR-۳۰۰ ionization chamber are ۱.۰۷۰۴ and ۰.۹۹۸۲, respectively.