The invention belongs to the field of gas purifiers and particularly relates to a nitrogen purifier and a nitrogen purifying method. The nitrogen purifier comprises a boiler, a reactor, a sealed water container and a drying cylinder, wherein two ends of the boiler are respectively provided with a gas inlet and a gas outlet, two ends of the reactor are respectively provided with a gas inlet and a gas outlet, the reactor is loaded with phosphorus powder, the sealed water container is provided with a gas inlet pipe and a gas outlet pipe, upper and lower ends of the drying cylinder are respectively provided with a gas inlet pipe and a gas outlet pipe, a plurality of silica layers are distributed in the drying cylinder from top to bottom, the boiler, the reactor, the water container and the drying cylinder are connected in order and the gas outlet pipe of the drying cylinder is connected to a collection tank. A manner of combining chemical reactions and physical adsorption is adopted to purify nitrogen containing oxygen and reducing gas. The whole process of the nitrogen purifier and the method is energy-saving and environmental friendly, and devices can be reutilized so that the nitrogen purifier and the method are energy-saving and environmental friendly.