The invention discloses a low temperature duvel for a superconducting magnet. The low temperature duvel for the superconducting magnet comprises a hollow annular barrel body, an upper end socket, a lower end socket and bearing rods, wherein the upper end socket and the lower end socket are respectively connected with the upper end and the lower end of the annular barrel body in a sealing mode and form a vacuum chamber together. A plurality of through holes are formed in the end sockets. The through holes are respectively used for installing a refrigerator nose and a suspender, and for signal lines, a vacuum gauge tube, a vacuum gauge outfit and a current lead line to penetrate. The bearing rods are used for lifting or supporting the superconducting magnet inside the vacuum chamber, and the number of the bearing rods is more than two. The invention further discloses a corresponding design method of critical size parameter of the low temperature duvel for the superconducting magnet. The low temperature duvel for the superconducting magnet has the advantages of bearing large stress in various working conditions, avoiding deformation or damage of a cover plate, and notably reducing occurrence of the heat leakage phenomenon. Besides, convenient and reasonable design index is provided in the process of designing the duvel of the same kind.