Abstract: Environmental-unfriendly power supply mode and fresh water shortage are two main problems for independent islands. A full renewable energy supply system is an effective solution to the above problems. Firstly, a 100% renewable energy supply system based on the water-electricity cogeneration of concentrating solar power（CSP） plants was proposed in this paper. By collecting the exhaust steam produced in the generation process and using it for water desalination, the cascade utilization of energy was achieved and the overall efficiency of the system was improved. The flexible dispatch ability of CSP plants was utilized to complement to wind power generation and reduce the energy storage configuration requirements for islands. The optimal planning model of the full renewable energy supply system was then established and solved. Simulation results show that the proposed supply system improves the efficiency of renewable energy utilization and capacity factors of renewable energy units; the peak load demand is cut down and the capacity configuration of units is also reduced. The cost-effectiveness of the proposed system is better.