Abstract: Referring to the thermal power plant DC unit and the pressurized water reactor standards as well as the operation experiences and in view of the secondary circuit structure and material features of the high temperature gas-cooled reactor, this paper studies three methods of controlling the secondary circuit water quality of the high temperature gas-cooled reactor, which include dosing control, the operation method of the condensate water polishing system and system flushing before unit start-up. In the end, the three methods are discussed in detail, and a scientific and complete method for optimizing the quality of water and steam in the secondary circuit of the high temperature gas-cooled reactor is formed. The method is discussed and approved by the experts, and is compiled into the commissioning outline and the operation rules for the high temperature reactor.