Embodiments of the present disclosure provide a gas purifying device and an ion migration spectrometer. The gas purifying device includes a first purificant vessel, a second purificant vessel and a valve communicated between the first purificant vessel and the second purificant vessel. The valve is configured to allow a gas flows from the second purificant vessel to the first purificant vessel in a first state and to permit the gas to flow from the first purificant vessel to the second purificant vessel in a second state.