The invention relates to a high-pressure dry air maintenance system and a high-pressure dry air maintenance method for a water vapor system of a power station. The high-pressure dry air maintenance system comprises a high-pressure air preparing system, a high-pressure air purifying system and a high-pressure dry air maintenance monitoring system. High-pressure dry air treated through water removal, oil removal and dust removal enters the water vapor system and is then discharged out of the water vapor system through a water vapor system exhausting air valve or a water drain valve to remove residual moisture in the water vapor system and reduce the relative humidity of the air in the water vapor system so as to achieve high-pressure dry air maintenance of the water vapor system. Compared with the existing low-pressure dry air maintenance technology, the high-pressure dry air maintenance technology adopted by the invention has the advantages as follows: the detachment of a large number of check valves in the water vapor system is not required, so that the workloads of detaching and recovering the check valves are reduced; the pipe diameter of an intake pipe is relatively small, so that the workload of mounting the intake pipe is reduced; difficulties in water sealing and air locking are overcome, and a dry air maintenance effect is improved. Through the use of the high-pressure dry air maintenance system and the high-pressure dry air maintenance method, the high-pressure dry air maintenance of the water vapor system of the power station can be achieved, stops and standby corrosions of the water vapor system of the power station are effectively reduced, and a guarantee is provided for the safe and economical operation of the power station.