Abstract: The sub-critical nuclear power reactor is composed by the Tokamak device in the center and the fission blanket surrounding it. A design layout of the fuel and coolant channel of the fission blanket was offered in the paper, in which the safety analysis was done. The CFD code was used for the thermal-hydraulic design and safety analysis of coolant channel blocked accident. The RELAP code was used to simulate the fission blanket of the sub-critical nuclear power reactor, and the inherent safety of it was researched. By the analysis, some safety weak points were found and related suggestions were provided for the future safety improvement of the sub-critical nuclear power reactor.