The present invention provides a Dewar for a superconducting power device. The Dewar comprises: a box for containing liquid nitrogen, wherein an open end is formed on the top of the box; a top cover hermetically connected with the open end of the box; an inner cylinder for the iron core post of the superconducting power device to pass through and arranged to pass through the box laterally; and first and second end plates mounted on the two lateral ends of the box, wherein both ends of the inner cylinder are fixedly connected to the first end plate and the second end plate respectively, and thebox, the top cover, and the inner cylinder are each configured as a double-walled structure with a vacuum heat insulation layer.