This study applies dynamic deformation analysis to the rake face stress distribution of cemented carbide cut-off tools by turning, using a finite element method. The results are following: 1. The dynamic loaded state of a cut-off tool was very changeable for the first 0.6 seconds. Reaching the normal state, it became in active. 2. Chipping was influnced not only by the magnitude of stress but also by the abrupt change of tensile and compressive stresses. 3. The distribution chat of principal stress by dynamic load and the direction of resultant vector were almost constant regardless of load time.