Flexibility and versatility in production put high demands on the planning, simulation and ramp-up of assembly systems and processes. For this purpose, a digital twin of a laser-based assembly assistance system for manual mounting tasks was developed, implemented and analyzed. A capability model was elaborated using quantitative and qualitative studies. The capability model was realized as a Unity 3D model. In the augmented reality implementation using the Microsoft HoloLens users can control the digital twin through hand gestures and voice control. The implementation shows that the digital twin of the laser-based assembly assistance supports the planning, simulation and training of employees at the shop floor.