Chinese Spallation Neutron Source (CSNS) is one of the key projects of China, in which the main magnet power supplies adopt the structures of resonant networks (Wang et al. in Sci China Phys Mech Astron 54(Suppl 2):239–244, 2011). Since each network contains a lot of components, and the working state of all the components will affect the whole accelerator, it is necessary to monitor the operation of each part in the resonant network. In this protections system, a supervision to 314 switch signals and 118 analog signals is realized using a chip of field programmable gate array (FPGA). The details about the hardware and software designs are introduced in this paper. This protection system has been used in CSNS project, and the result proves that the RCS has been well monitored by this system. This system is a self-developed protection system according to the engineering needs of CSNS. It can realize the real-time monitoring and protection of the working state of resonance network by processing a large number of data using FPGA.