There is a high demand to conduct high performance machining in industry to produce high quality parts with high efficiency. Thus, physical machining simulation is a must. Many researches have been conducted on machining simulation with the finite element analysis method. However, the prior machining simulation method is not completed, and the results are not reliable. In this thesis, a completed and accurate method of machining simulation is proposed. First, the cutting tool and the workpiece 3-D solid models are accurately built. These are often ignored in the prior methods. Second, the tool and the workpiece models are set up in the Thirdwave System machining simulation software according to the actual tool location and orientation in machining. Third, the adaptive meshing method is employed, and the mesh size is adapted for high accuracy and efficiency. Then, this approach is applied to a slender shaft turning. A detailed discussion on the constitutive equation for simulation is provided for more accurate results. The experiment results are used as a reference for the simulation model to improve the precision. Finally, the parameters for turning the slender shaft are optimized according to the simulated cutting temperatures and forces. The approach can be directly used in industry for high performance machining.