The invention relates to a multiscale fissioning core visualization method based on an automatic merging hierarchical structure tree. The visualization method is used in fission reactor design to check the correctness of the design of a reactor core which has been constructed or is being constructed. Based on the hierarchical feature of a fission reactor, a user input model is analyzed, grouping of a hiberarchy relation structure is established intelligently, a corresponding rendering unit is generated based on grouping, an overall rendering tree structure is established, and quick visualization of an area in which a user is interested is achieved; visualization speed is increased greatly, real-time visualization during modeling of a fine reactor core model is realized, and then fissioning core modeling efficiency is improved remarkably.