Wire-arc based metal big area additive manufacturing (mBAAM) enables one to print a part up to approximately 10 feet tall owing to its superior feature of high deposition rate and minimal material waste. The printing often takes days or even weeks to complete. For a wide adoption of this manufacturing process for critical structural components, tight process control for the desired microstructure and part properties is primarily required. Under dynamic printing conditions and complex part geometries, part deformation is primarily associated with varying thermal cycles influencing phase transformation and internal stress buildup. This can reduce the local part strength causing cracking or catastrophic failure of structural component. A large scale thermo-mechanical simulation has built and tested Oak Ridge National Laboratory (ORNL) and Dassault Systems to manage thermal cycles, part distortion, and residual stresses. First, two thin-wall structures were printed, and temperature history and process parameters were recorded for model calibration and validation. The part distortion and residual stress were measured using High Flux Isotope Reactor (HFIR) neutron beam diffraction and compared with the predicted simulation results. Then, the model capability is used to demonstrate and understand the effect of various printing conditions, including power, speed, tool path, and multi-heat sources on microstructure and part performance. Various melting sequences (e.g., horizontal, vertical, honeycomb, etc.) and sets of process parameters (e.g., multi-heat sources) are explored using finite element method (FEM). Metallurgical transformation model is used to predict the corresponding evolution of microstructures (e.g., fraction change of each phase) during and after printing. Finally, we suggest a possible solution to mitigate the inhomogeneity of microstructure, distortion, and residual stress for large-scale components.