The utility model discloses a hydrogen purity measurement device for a hydrogen-cooled generator. The hydrogen purity measurement device for the hydrogen-cooled generator comprises a gas purity transducer, a hydrogen source branch and a replacing gas branch, wherein the gas purity transducer is provided with a gas inlet and a gas outlet, the gas inlet of the gas purity transducer is connected with a hydrogen sampling gas path, the hydrogen sampling gas path is communicated with a generator room of the hydrogen-cooled generator to sample and measure hydrogen inside the generator room, one end of the hydrogen source branch is communicated with the hydrogen sampling gas path, the other end of the hydrogen source branch is communicated with a hydrogen source, one end of the replacing gas branch is communicated with the hydrogen sampling gas path, the other end of the replacing gas branch is communicated with a replacing gas source, and switching valves which are used for controlling connection and disconnection of corresponding branches are arranged on the hydrogen source branch and the replacing gas branch respectively. The hydrogen purity measurement device is capable of filling source hydrogen and replacing gases into the generator room when necessary, so that a gas filling device which is arranged separately can be cancelled, a sealing structure of the gas filling device can also be cancelled, and the production cost of users can be reduced.