Abstract: Specific absorbed fractions of target organs were calculated by MCNP4C, source organs were lungs which were divided into right lungs and left lungs．The comparison results for various adult male models, various ages models and gender models show that children’s are higher than adult’s, and female’s are higher than male’s about specific absorbed fractions．When target organs and source organs are same, specific absorbed fractions decline from 0.01 to 0.05 MeV；on the contrary, the specific absorbed fractions increase from 0.01 to 0.05 MeV．From 0.05 to 4 MeV, various organs incline to a constant value．