Complex thermodynamic cycle systems play a critical role in advanced energy applications, where modeling and simulation constitute a fundamental component of Model-Based Systems Engineering (MBSE). Conventional sequential modular approaches rely heavily on predefined calculation sequences and empirical parameter settings, leading to limited adaptability for complex cycle topologies with strong coupling, flow splitting, and multiple recuperation processes. This study proposes an equation-oriented (EO) modeling framework for thermodynamic cycle systems, in which the entire cycle is formulated as a coupled nonlinear algebraic equation system and solved simultaneously. Standardized algebraic component models are established for compressors, turbines, and recuperators. An ε–NTU-based heat exchanger formulation is adopted to avoid the predefined minimum temperature difference commonly required in conventional approaches. In addition, a bi-level solution strategy combining outerlayer parameter scanning and inner-layer Newton iterations is introduced to handle additional design degrees of freedom. The proposed framework is validated using supercritical CO₂ simple recuperated and recompression Brayton cycles. Simulation results show that the predicted cycle efficiencies agree well with published reference data, with deviations below 1% under all investigated operating conditions. The framework demonstrates stable convergence behavior and strong adaptability to complex thermodynamic topologies. The proposed approach exhibits acausal, modular, and topology-decoupled characteristics consistent with the declarative modeling philosophy of Modelica. It provides a unified and extensible solution framework for MBSEoriented modeling and simulation of complex thermodynamic energy systems.