Abstract: To tackle several engineering challenges of vacuum coating robots, including the inability to directly observe equipment inside the sealed vacuum chamber, delayed feedback of process information, and high material costs for offline trajectory verification, this paper designs and implements a lightweight virtual-real synchronous digital twin monitoring system. The 3D simulation of the system is realized based on Unity3D. The C# programming language combined with the open-source S7.Net communication library is adopted to achieve bidirectional Ethernet data exchange between the upper control computer and PLC. Through 3D modeling of the entire robot, mesh optimization, parent-child joint binding and motion drive design, an integrated virtual simulation scene covering mechanical movements and coating processes is constructed. The system can collect and visually display key process data in real time, such as the five-axis pose of the robot, target gun status and target power supply parameters. It supports multi-angle view switching, offline trajectory preview, collision warning and other functions. The proposed scheme does not require authorization for commercial industrial simulation software, and can run stably on ordinary industrial personal computers with free Unity3D, which is applicable to application scenarios such as online monitoring and process preview of magnetron sputtering coating production lines.