Abstract: The subcooled liquid nitrogen cooling circulation system for superconducting cables is a main sub-system in the three-coaxial high-temperature superconducting cable test device. According to the operating parameters and load requirements of the cable, the process design of the subcooled liquid nitrogen cooling circulation system and the structural design of cold box and pressure control device are finished. The flow resistance is analyzed and calculated to choose the liquid nitrogen pump that matching the hydraulic curve. Combined with the heat load required by the cable, the immersion coil heat exchanger in the system is designed and calculated. The on-line test results show that the design meets the cooling requirements.