Superconducting magnetic energy storage (SMES) system has been proven very effective to improve power system stabilities. It is realized with superconductivity technology, power electronics and control theory. In order to promote the applica-tion of such kind control device and to further investigate the properties of the controller, a detail mathematic model of such control device is developed. Based on the developed model, extensive analysis including time domain simulation is carried out to investigate the characteristic of the SMES to compensate the unba- lanced dynamic active and reactive power of AC power system. The capability of SMES to increase power system transient and small signal perturbation stabilities are analyzed. A prototype SMES is developed, in which the conduction cooling and the high temperature superconductive techniques are used. The performance of the prototype is experimentally investigated in a laboratory environment. Very en-couraging results are obtained. After a brief introduction of the SMES control sys-tem and the principle of its capability to improve power system stabilities, the de-tails of the mathematic model, the theoretical analysis, the developed device and the experiment test results are all given in this paper. Superconducting magnetic energy storage (SMES) system has been proven very effective to improve power system stabilities. It is realized with superconductivity technology, power electronics and control theory. In order to promote the applica- tion of and kind of control device and to further further the based on the developed model, extensive analysis including time domain simulation is carried out to investigate the characteristic of the SMES to compensate the unba- lanced dynamic active and reactive power of The capability of the SMES to increase power system transient and small signal perturbation stabilities is analyzed. A prototype SMES is developed, in which the conduction cooling and the high temperature superconductive techniques are used. The performance of the prototype is experimentally investigated in a laboratory environment. Very en-couraging results are obtained. A fter a brief introduction of the SMES control sys-tem and the principle of its capability to improve power system stabilities, the de-tails of the mathematic model, the theoretical analysis, the developed device and the experiment test results are all given in this paper .