In the process of tunnel excavation, rocks with great hardness and abrasion are often encountered, which leads to low rock breaking efficiency and serious tool wear. In order to solve this problem, a new TBM cutting mechanism is proposed in this paper. The cutter head is equipped with a plasma torch and a shield cutter. With the help of plasma flame, the rock surface is heated to expand its cracks, thus reducing the rock strength, reducing the wear of the mechanical cutter and improving the service life of the mechanical cutter. In addition, the structural strength of cutter head and the reliability of transmission mechanism are simulated. The temperature field and jet field of plasma moments with different structures are simulated. The analysis results show that the new plasma-assisted TBM cutting mechanism can meet the application requirements.