Though a lot of research works have been done, some key technologies of finite element simulation have not been resolved completely. A detailed finite element model of high speed orthogonal cutting of titanium alloy Ti6Al4V is developed. Several mechanics models of cutting process, such as material constitutive model, chip separation model and chip damage model, are implemented to improve finite element simulation accuracy. The chip shape and cutting force agree well with experimental results, which show the finite element model developed in this study is reasonable. Using this finite element model, chip formation process of titanium alloy Ti6Al4V is simulated. Results indicate that the material between the shear bands is only weakly deformed, and the deformation is stronger on the tool side of the chip. This work will be a base for process parameter optimization, tool’s optimization selection and design during high speed cutting of difficult-to-cut titanium alloy.