Application and research status of cast steel is introduced in steel structure, especially in steel frames. A cast modular joint and its design approaches are proposed, appropriate for rectangle or square tubular column to H-beam connections. The cast modular joint is conceived base on the concept of utilizing stable plastic dissipation of panel zone. Nonlinear finite element analysis is conducted to simulate monotonic loading and cyclic loading of the cast modular joint and traditional welded connections. Rupture Index is introduced to evaluate the propensity for ductile fracture initiation of different joints under large plastic deformation. Energy dissipation features are analyzed and demonstrated from multiple aspects, including stiffness, load carrying capacity, ductility, energy dissipation capacity, energy dissipation mechanism and plastic deformation modes. Research shows that the proposed cast modular joint exhibits better seismic performance than traditional welded connections, with sufficient developed dissipation capacity of seismic structure system on the premise of no ductility loss.