Today, smart manufacturing systems (SMS) are being developed to improve manufacturing competitiveness. Digital manufacturing (DM) is a technology that supports the carrying-out of tasks and decision-making based on digital models and simulation in a virtual environment, without physical prototypes or experiments. A DM system helps in the design and redesign and analysis of a factory, sustainably and efficiently, to optimize its performance in an SMS. In this paper, the contributions of DM systems in SMS and the application barriers of DM systems are described. A real case that has been developed to overcome the barriers is introduced. Finally, future directions of DM systems in SMS are discussed.