Based on the hybrid Chinese reference adult female phantom, the Chinese reference female boundary representation (BREP) phantoms involving sitting, walking, and squatting postures were established. The photon effective dose conversion coefficient (ECCK) and some organ absorbed dose conversion coefficients (DCCK) were calculated under six standard irradiation geometries, and the irradiation source included 20 monoenergetic photon energies ranging from 0.01 MeV to 10 MeV. The results indicate that the postures, location of the organs, and irradiation geometries have an impact on the dose conversion coefficients. With the same irradiation geometry, the DCCKs of different organs are different; when the photon energy is from 0.02 MeV to 0.1 MeV, significant differences exist in the DCCK of phantoms of various postures, and the maximum relative deviation is 80%. For the ECCKs, there are greater differences among phantoms of various postures with the same irradiation geometry when the photon energy is from 0.02 MeV to 0.05 MeV, and the maximum relative deviation is about 20%.