Digital manufacturing is a technology to simulate the real manufacturing process using the virtual model representing the physical schema and the behavior of the real manufacturing system including resources, processes and product information. Therefore, it can optimize the manufacturing system or prevent the bottleneck processes through the simulation before the manufacturing plan is executed. This study presents a method to apply the digital manufacturing technology for the steel cutting process in shipyard. The system modeling of cutting shop is carried out using the IDEF and UML which is a visual modeling language to document the artifacts of a complex system. Also, virtual NC simulators of the cutting machines are constructed to emulate the real operation of cutting machines and NC codes. The simulators are able to verify the cutting shape and estimate the precise cycle time of the planned NC codes. The validity of the virtual model is checked by comparing the real cutting time and shape with the simulated results. It is expected that the virtual NC simulators can be used for accurate estimation of the cutting time and shape in advance of real cutting work.