In this paper, a Multi-resonant-core-based (MRC) Series-parallel (SP) Resonant Switched-capacitor Converter (RSC) was proposed. On the basis of the traditional SP Switched-capacitor Converter (SCC), resonant tanks are incorporated. The on-time fixed frequency modulation is adopted, then the resonant inductor current in one resonant tank is overlapped with the others. By adding the overlapped period, the conversion ratio of the MRC SP RSC can be regulated continuously, widely and efficiently even at light load condition. In addition, the ZCS turn-on for all transistors and ZCS turn-off for all diodes are achieved. The large intermediate capacitor banks are replaced by the small resonant capacitors due to the complete resonance operation. A 4X MRC SP RSC was designed and built to verify the operation principle and regulation capability.