The work aims to meet the research, development and maintenance of offset printing machines, and to provide a self-presenting virtual platform for products. With PZ1740E four-fold single sheet monochrome lithographic offset press as an example, a more accurate measuring tool was used for actual measurement, then the modeling and its optimization were completed in the software 3ds MAX. And finally the production of the virtual assembly system was completed in Unity 3D. The assembly system was able to separate and assemble the printed part of the offset press both automatically and manually, showing the internal and external structure of the printed part. The combination of the virtual reality technology, assembly technology and offset printing machine present the overall structure and function of the printing part of the offset printing machine in a digital way. It can be better applied to the industrial design, improvement and maintenance of offset presses.