Combination of digital twin and manufacturing field is increasingly close. Digital twin can help machine tools achieve autonomous monitoring, evaluation and reasoning in an intelligent manufacturing environment and significantly improve intelligence. In this paper, we develop a digital twin intelligent monitoring platform for the milling process of machine tools, which can realize real-time interaction between the physical manufacturing process and its virtual data model. In order to realize the bidirectional connection between different modules and between the physical machine and the virtual model, the data acquisition module and the digital twin monitoring platform are built based on the idea of hardware abstraction layer development and integrated with the open CNC system. The digital twin monitoring platform has the features of loose coupling, modularity and easy expansion, which integrates the data analysis twin model built by dynamics analysis model and artificial intelligence algorithm. It can realize the functions of milling chatter identification and suppression, surface topography prediction, etc. The machining experiments have been verified to demonstrate the good performance of the monitoring platform in the actual manufacturing environment.