Titanium alloys are known for their strong chemical reactivity with surrounding gas due to their high chemical affinity, especially in dry machining. This paper describes a study of chip formation characteristics under nitrogen gas media when machining Ti6Al4V alloy with WC-Co cemented carbide cutting tools at high cutting speeds. Based on the experimental study, a finite element model of two-dimensional orthogonal cutting process for Ti6Al4V alloy at different cutting conditions was developed using a commercial finite element software Deform-2D. Saw-tooth chips with adiabatic shear bands were produced in both experiments and simulations. And the enhanced cooling and anti-frictional effects of nitrogen gas upon the high speed cutting process of Ti6Al4V alloy were analyzed. Results of this investigation indicate that the anti-frictional performance of nitrogen gas has a significant effect on chip formation when machining Ti6Al4V alloy at high cutting speeds. Compared to air, Nitrogen gas is more suitable in improving the contact conditions at chip-tool interfaces and in increasing the shear band frequency of chip formation during high speed cutting of Ti6Al4V alloy.