The change of size, surface roughness, residual stress, and so on profoundly influence the final machining quality of complex mechanical products. Digital twin machining technology can ensure machining quality by observing the machining process in real time. However, the current digital twin systems mainly adopt the display method of virtual-real separation. It leads to transmitting the useful processing information to the on-site technicians ineffectively, limiting the digital twin system to help field processing. The monitoring technology on the machining process by augmented reality based on the digital twin machining system is proposed to deal with this problem. Firstly, the augmented reality dynamic multi-view is constructed based on multi-source heterogeneous data. Secondly, the augmented reality is integrated into the real-time monitoring of the intermediate process of complex products to promote cooperation among the operators and the digital twin machining system. It can avoid irreparable errors when the finished product is nearly completed. Finally, the effectiveness and feasibility of the proposed method will be verified by a monitoring application case. © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.