Abstract: This paper introduces a high RF power coupling system for ion source application to national large-scale scientific facility CSNS, including the system architecture, RF system metrics calculating, assigning and implementing.This paper focuses on the designs of RF power amplifier, isolation transformer, impedance converter, auxiliary power supply, control & monitor and cooling system.It also discusses the structure and thermal designs in detail and gives the development results of a 80 kW RF power at the least at last based on careful analysis of the characteristic of the RF power coupling system.