Abstract: Superconducting maglev is one of the important engineering applications of high temperature superconducting magnets. Traditional cooling methods, such as chiller conduction cooling and liquid helium immersion cooling, cannot operate independently after being detached from the cooling source. They exhibit significant temperature gradients, have high operational costs, and are difficult to adapt to complex dynamic vehicle environments. The presence of solid nitrogen can reduce the temperature gradient in superconducting magnet systems and enhance temperature uniformity. Additionally, the high specific heat capacity of solid nitrogen, along with its second-order phase transitions, allows the superconducting magnet system to operate independently when detached from the cooling source, improving system portability. Furthermore, when liquid nitrogen transforms into solid nitrogen, it can bond with the superconducting magnet, increasing the system's dynamic stability. The solid nitrogen cooling system employs a cooling machine for pre-cooling and solid nitrogen for insulation, providing a wide operational temperature range and good thermal uniformity. This setup offers a low-temperature working environment for high-temperature superconducting magnets while enhancing the magnet’s dynamic performance and adapting to vehicle-mounted conditions. Cooling time, offline time, and re-cooling time are the key indexes of solid nitrogen cooling system for superconducting electromagnet. The composition and operation process of the system are described in detail, and the heat leakage of the system is analyzed theoretically. The transient thermal analysis model of the system is established, which can calculate the temperature distribution of the system cooling process, offline operation process and re-cooling process. The temperature change of the system cooling process, offline operation process and re-cooling process is simulated. The simulation results show that the magnet temperature drops below 30 K, and the system can run offline for 2 hours at no more than 40 K temperature. Based on the calculation results of the model, the system is optimized. The model can provide reference and guidance for the design and optimization of solid nitrogen cryogenic system.