Composite liquid helium dewar with liquid nitrogen cold shield

The invention discloses a composite liquid helium dewar with a liquid nitrogen cold shield. The composite liquid helium dewar with the liquid nitrogen cold shield comprises an inner cylinder, a middlecylinder, an outer cylinder and a low-heat-leakage plug, wherein the inner cylinder, the middle cylinder and the outer cylinder are made of a composite, and the low-heat-leakage plug is made of a composite and the like. The outer cylinder is used for keeping vacuum. The middle layer is used for storing liquid nitrogen. The inner cylinder is used for storing liquid helium. The space defined by themiddle cylinder, the inner cylinder and the outer cylinder can keep the high vacuum degree which is smaller than or equal to 10 Pa for a long time. Cylindrical shells and lower base plates of theinner cylinder, the middle cylinder and the outer cylinder are woven from fiber and formed through curing of vacuum pressure impregnation epoxy resin. The gas gap rate of the obtained composite is smaller than 1%. Multiple lay