Joint maintenance method for secondary circuit steam path system of high-temperature gas cooled reactor nuclear power unit

The embodiment of the invention provides a combined maintenance method for a secondary circuit steam path system of a high-temperature gas cooled reactor nuclear power unit. The combined maintenance method comprises the steps of maintenance preparation, maintenance boundary establishment and maintenance input and monitoring, gas is provided for a main steam system and a steam turbine, and the steam exhaust pressure of a low-pressure cylinder and the pressure of a condenser are made to be at preset pressure values by controlling the gas supply amount; and the air outlet volume and humidity of each monitoring port are obtained, the air outlet volume of each monitoring port is made to be at a preset air volume value by adjusting the air supply volume, the drain valve and the water drain valve are closed after the humidity of each monitoring port is smaller than the preset humidity, the exhaust valve is adjusted to be at the preset opening degree, and the air supply volume is adjusted to be at the preset air supp