According to the requirements of high-energy particle accelerators, a cryostat system was designed and manufactured to provide a low-temperature environment for high uniformity superconducting magnet used for calibration. The performance test of the calibration magnet system including linearity, locking area, stability, and uniformity was completed. This system uses a single 1.5 W @ 4.2 K refrigerator by combining direct conduction cooling with indirect conduction cooling of the gravity heat pipe. The superconducting magnet was cooled to 4 K and entered the superconducting state, and the minimum temperature reached 2.8 K within 40 hours. The maximum excitation current is 300 A and the maximum magnetic field reaches about 6.2 T. At present, the equipment has been running stably for more than 90 days.