The invention discloses an online gas collecting and exhausting device for nuclear power station fluid system non-condensable gas. The online gas collecting and exhausting device comprises a gas collecting tank, a gas collecting pipeline, a gas collecting valve, a water injection valve, a water injection pipeline, a gas exhausting pipeline, an exhaust valve, a hydrophobic pipeline and a hydrophobic valve, wherein the gas collecting pipeline and the gas collecting valve are connected to the bottom of the gas collecting tank, the water injection valve and the water injection pipeline are connected to the gas collecting tank from upstream, the gas exhausting pipeline and the exhaust valve are connected to the top of the gas collecting tank, and the hydrophobic pipeline and the hydrophobic valve are connected to the gas collecting pipeline. In addition, the invention further discloses an online gas collecting and exhausting method for the nuclear power station fluid system non-condensable gas. Compared with the prior art, the online gas collecting and exhausting device for the nuclear power station fluid system non-condensable gas has the advantages of being simple in structure, convenient to operate, suitable for nuclear power station fluid systems different in pressure and fluid, and capable of effectively avoiding system outage and radioactive fluid leakage.