The invention belongs to the key technical field of million kilowatt level advanced pressurized water reactor nuclear power plants, and discloses a nuclear power plant generator whole air tight test method. The test method includes that gas is inflated into a generator and a hydrogen system, the pressure is increased to working pressure to be maintained, a leakage point is detected to be handled, the test can be finished when pressure maintaining time of leakage rate meets a predetermined requirement and is larger than or equal to 24 hours, and mixed gas of air and hydrogen is inflated to the generator and the hydrogen system. The test method further comprises a temperature control operating step and an anti-oil-swapping operation step, wherein the temperature control operating step is used for maintaining balanced temperature inside the generator, and the anti-oil-swapping operation step is used for controlling swapping of sealing oil on the airside and the hydrogen side not to cause gas leakage. The test method further comprises sealing oil tank liquid level monitoring step in the process of pressure maintaining. Recording duration for monitoring of gas temperature, pressure, ambient atmosphere pressure and sealing oil tank liquid level inside the generator is every 20-40 minutes in the process of the pressure maintaining. The nuclear power plant generator whole air tight test method is short in time limit for construction and high in test precision.