Quench protection is a key technology for the practical application of superconducting magnetic energy storage (SMES). In this paper, a digital quench protection system has been developed for a kJ class SMES hybrid magnet fabricated by YBCO and BSCCO at China Electric Power Research Institute. The digital signal processing technology is adopted to realize the algorithm. It can trigger output signal that is used to activate the protection circuit and control the magnet ramp down in the event of a quench. Also, the human machine interface is developed, which is used to monitor the operating states of the operating environment, quench protection circuit and superconducting magnet. Finally, the quench protection system passed the SMES dynamic simulation experiment.