The mechanical properties of carbon fiber, especially tensile modulus, are closely related to the orientation of crystals. Hence, the stretching of carbon fiber during carbonization is of importance. In this study, the tension arm between the carbonization furnaces was used to stretch carbon fiber. The relationships among the stretching tensions of the first stage carbonization (< 800 degrees C) and the second stage carbonization (> 1200 degrees C), the aromatization index for oxidized polyacrylonitrile fiber, and the properties of carbon fiber are discussed.