A method for determination of tool-chip contact length is theoretically presented in orthogonal metal machining. By using computer simulation and based on the analyses of the elastro-plastic deformation with lagrangian finite element method in the deformation zone,the accumulated representative length of the low layer, the tool-chip contact length of the chip contacting the tool rake are calculated, experimental studies are also carried out with 0.2% carbon steel. It is shown that the tool-chip contact lengths obtained from computer simulation have a good agreement with those of measured values.