The real-time simulation of a line-commutated converter-high voltage direct current (LCC-HVDC) system based on a field programmable gate array (FPGA) is proposed to meet the increasingly complex dynamic characteristics and real-time simulation requirements of HVDCs. In addition, a real-time simulation platform based on a CPU + FPGA is established forsimulation verification. First, a simulation model of the 12-pulse rectifier of an LCC-HVDC is established using the compact nodal analysis method (C-NAM). When compared with the traditional node analysis method, C-NAM reduces the number of multiplication executions in a single simulation step, and the degree of program serialization is signifi cantly reduced,which greatly improves the real-time simulation speed of a FPGA. Then, this simulation model is programmed in a FPGA, and the optimization algorithm further shortens the simulation step size. Finally, a 12-pulse LCC-HVDC is compared and verified with a 1 μs simulation step on a FPGA real-time simulation platform, and a simulation analysis verifies the accuracy of the model. This method can improve the simulation scale of an LCC-HVDC system, and enhance the versatility of the LCC-HVDC real-time simulator based on a FPGA.