Carbide cutting tools in the cutting process crack damage has been caused by processing problems plagued the people a correct understanding of the causes of cracks and to take appropriate preventive measures are the key tool to improve working life and cutting performance. Relevant research literature indicates that when cutting at high cutting speeds, the tool is easy to produce thermal cracks and edge chipping phenomenon will increase. This paper analyzes the mechanism by cutting test and interrupted cutting carbide tool cracks found in the cutting cycle of the heating phase, compression heat stress can cause narrowing in the positive zone on the rake face of the cutting blades with local plastic deformation, then when the narrow zone in the outside world elastic material impact forced cooling again, there will be enough to cause visible cracks tensile stress, which verifies the thermal stress caused arguments carbide Tool main cause cracks.