In response to the challenges of bearing fault diagnosis, this paper constructs a fault diagnosis architecture based on digital twin. In the physical layer, a bearing test bench and sensors are used for data collection, and data fusion is achieved through transformation and encapsulation. The data layer relies on the OPC UA communication protocol to complete data interaction and synchronous mapping, generating twin data. In the virtual layer, 3D modeling and rendering are carried out, and then the model is imported into Unity 3D to realize the virtual mapping of the physical entity. On this basis, the fault diagnosis module uses order analysis and result encoding to obtain image data, and combines with a deep - learning model for fault diagnosis. This architecture realizes the coordination of the physical layer, data layer, and virtual layer, which is expected to improve the accuracy and real - time performance of bearing fault diagnosis, and provide effective support for the predictive maintenance of industrial equipment.