As the pivotal equipment connecting the primary and secondary loops of pressurized water reactor nuclear power plants, the dynamic thermo-hydraulic characteristics of the nuclear steam generator are directly related to the safe and stable operation of the unit. However, traditional modeling approaches suffer from poor versatility and low efficiency, making it difficult to meet the R&D demands for diverse application scenarios and iterative optimization. Addressing these bottlenecks, this paper proposes a modular modeling and dynamic simulation method for nuclear steam generators based on the Modelica language. First, based on a hierarchical modeling approach, component-level models covering plena, pipes, heat structures, steam-water separators, and feedwater plena are constructed to achieve free configuration and visual simulation modeling. Second, according to the operating principles and structure of the nuclear steam generator, a complete dynamic simulation model is assembled using these component-level models. Finally, the established model is validated against the RELAP5 code to verify the effectiveness and reliability of the proposed method. The results indicate that the Modelica-based steam generator simulation model combines high accuracy with high efficiency, providing significant technical support for the rapid design and verification of nuclear power systems.