Nuclear energy seawater desalination is a unique technology for the production of freshwater - especially potable water - on a large scale without contributing to greenhouse gases, SOx or NOx etc., which use existing nuclear power plant (NPP) technology and seawater desalination technology. The scarcity of freshwater and especially potable water is jeopardizing many regions of the world. It is estimated that about three-quarters of the world's population may suffer from high or moderate water shortages, with a focus on North Africa, the Middle East, Latin America and South-east Asia. The clean development mechanism (CDM) creates a unique, market-based means by which signatories to the Kyoto Protocol, who are required to comply with emission limitations, can work with developing partners in achieving global reductions in greenhouse gases, while promoting those partners' sustainable development by providing financial and technology assistance. In essence, CDM creates a means for transferring the credit for reducing emissions from projects in developing countries to the sponsors of those projects in developed states. A comparative economic analysis of nuclear seawater desalination was carried out under the CDM. The results were calculated by a desalination economic evaluation program (DEEP2.0) developed by the International Atom Energy Agency which included a pressurized light water reactor (PWR), a pressurized heavy water reactor (PHWR), a combined cycle gas turbine (CC) and an open cycle gas turbine (GT), in a middle scale of about 600 MWe, and two desalination technologies: reverse osmosis (RO) and multi-effect distillation (MED). The CDM in nuclear seawater desalination cases was realized in quantitative terms, which are carbon taxes of roughly $40-80/t (of carbon), whose sum is equivalent to the annual total thermal production of nuclear power plants on the same scale as coal-fired plants. The calculated results indicated a significant economics benefit for nuclear seawater desalination.