In the multi-stage acceleration of heavy ions such as the acceleration at the RIKEN RI beam factory (RIBF), the electron stripping process with charge strippers is an inevitable process for the efficient acceleration. The efficiencies, however, for the charge-state conversion of very heavy ions are not so high with common charge strippers in the acceleration up to the energy around hundreds MeV/u. The total efficiency of two charge strippers for 238U acceleration at the RIBF is only 6%. It is a bottleneck for the intensity upgrade. In the present study, we designed high-efficient charge stripper rings which have applicability to the RIBF.