Numerical codes based on the model of ion confinement and losses in the electron cyclotron resonance (ECR) source have been applied to the mathematical simulation of krypton and xenon ion production in the 18 GHz ECR ion source at RIKEN. An equation of complete plasma energy is introduced to estimate the rf power of the ECR plasma heating. The final result of fitting is in reasonable agreement with the real experimental data for the Kr and Xe ion production in the source and used to estimate the main plasma parameters. ©1998 American Institute of Physics.