Due to its characteristics of quick response and high power density, superconducting magnetic energy storage (SMES) system has bright future of applications in power system. The principle, components and key technology of SMES are discussed in this paper. The development trend of SMES is analyzed from three aspects of apparatus, application and control, it is pointed out that SMES will develop toward modularization and decentralization, and SMES can also form hybrid energy storage system with other energy storage system. Based on the influence of the magnet current and thermal stability of superconducting magnet on the power response characteristic of SMES, it is proposed to conduct SMES status evaluation and control strategy optimization during SMES operation. At last, factors restricting the development of SMES are summarized.