Provided is a method for measuring flow of air leaked into a condenser and a vacuum system. Firstly, under the rated load working condition of a turbo generator set, a vacuum leakage test is carried out, and the decrease rate of vacuum is measured; then, according to the relational expression of the flow of the air leaked into the condenser and the vacuum system and the decrease rate of the vacuum, the flow of the air leaked into the condenser and the vacuum system is calculated through the measured decrease rate of the vacuum. According to the method, the fact that the flow of the air leaked into the condenser and the vacuum system is measured through the decrease rate of the vacuum is achieved, meanwhile, the leakproofness level of the condenser and the vacuum system is quantified, and the defect that the flow of the air leaked into the condenser and the vacuum system is not easy to measure directly is overcome.