Aiming at the problem of nitrogen being mixed in LNG, the practical significance and research value of its harm are expounded, and the nitrogen detection technology and separation technology of LNG are researched. The nitrogen detection in LNG can be carried out in three aspects: accurate measurement, on-site simple observation judgment, and on-site combustible gas concentration measurement judgment. The representative separation methods of nitrogen in natural gas are respectively selected to introduce in four aspects: deep freezing, solvent absorption, and pressure swing adsorption and membrane separation. The proposed methods will be helpful to select the appropriate nitrogen separation technology, and will also have certain reference significance for the nitrogen content detection of LNG.