The invention relates to a quick helium mass spectrum leakage detecting device for a diaphragm inner circle welding joint, solves the problem of difficulty in sealing caused by a small inner cavity formed due to a thin wall and welding of the inner circle welding joint, effectively avoids the problem the whole diaphragm box is scrapped due to leakage of inner circle welding joint, and improves theleak detection efficiency greatly. An inner supporting tool, an upper cover and a lower cover, a sealing ring and the like are used for sealing a narrow space formed after the diaphragm inner circlewelding joint is welded, so that quick and accurate helium mass spectrum leakage detecting is realized; compared with the prior art, the inner supporting tool, the upper cover and the lower cover, thesealing ring and the like are used for sealing the narrow space formed after the diaphragm inner circle welding joint is welded, so that diaphragm inner circle welding joint leakage detecting is realized, and the possibility that the whole diaphragm box is scrapped due to leakage of the weld joint of the diaphragm is reduced.