Abstract: AP1000 as the third generation of nuclear power units,requires its operation water to be below 50ppm of TOC as described in its Chemistry Manual.TOC contained in Demineralized Water（DW） is mainly the residual of the process of DW raw water pre-treatment.Another source of TOC is owing to decomposition of the organic materials in the system.When exposed to high temperature or radiation,TOC yields organic acid which will corrode metallic materials.TOC contained in DW can be effectively removed by operations of mixed condensing,reverse osmosis（RO）,ultra-violet ray radiation,and etc.