The utility model relates to an island energy supply system. The island energy supply system comprises an LNG power generation system unit, a renewable energy power generation and energy storage unit and a low-temperature multi-effect distillation sea water desalination system. The island energy supply system is a combined island energy supply system formed by a renewable energy power generation and energy storage system based on an LNG generator and unstable energy such as wind energy, solar energy and wave energy, waste heat of the system serves as a heat source of a sea water desalination unit. In the energy storage process, stored LNG is converted into high-pressure NG through cold storage gasification, and enters an NG storage tank and a pipe network system to be stored for use; secondly, energy of indirect cold of air compression is recycled through cold accumulation, throttling is carried out, and then compressed air is liquefied and stored. In the electricity utilization process, the high-pressure NG enters a turbine expander to do work after absorbing heat to be warmer, and then the high-temperature NG enters a small gas turbine combustion chamber to combust with the compressed air so as to drive a gas turbine to do work; liquid air enters the turbine expander to do work after being processed through cold accumulation and gradually absorbing heat to be warmer. The island energy supply system can supply electric energy and fresh water to an island at the same time, the unstable renewable energy is converted into stable controllable power generation output, the purposes of improving system efficiency and reducing electricity utilization cost are achieved, and the island energy supply system has great advantages compared with a traditional island energy supply system.