Abstract: In order to implement full-core and real-channel-resolved parallel subchannel simulations, a subchannel-based parallel partitioning and mapping method was presented. The method is able to partition either a full-core or a single assembly, and it maps the computation tasks and processes flexibly. The method chooses the appropriate partitioning method according to the core number of the computers/clusters used, which enables the full-core thermal-hydraulic simulation to be carried out on various computing environments ranging from personal computers to supercomputers. A full-core and real-channel-resolved steady simulation, which analyzes 157 assemblies with each subchannel divided into 125 layers axially, is carried out on the Tianhe Ⅱ supercomputer using 4-6 280 cores. The running time is about 22 h using 4 cores and the running time is 470 s using 6 280 cores. By utilizing hybrid parallel computing, the running time on 6 280 cores is reduced to 397 s.