Abstract: Referring to the water quality standard of the pressurized water reactor (PWR) second circuit and the thermal power direct current furnace, combined with the structure and material characteristics of the second circuit of the high temperature reactor, this paper updated the original intake and outlet water standards of the steam generator (SG) in the high temperature reactor and obtained a more reasonable water quality control standard. And then this paper researched three methods of controlling the secondary circuit water quality of the high temperature gas cooled reactor, i.e., the system flushing before unit start-up, the dosing control and the control of operation of condensate water polishing system. In the end, the three methods are discussed in detail, and a scientific and integrated method for optimizing the quality of water and steam in the second circuit of high temperature reactor was presented.