The Raman spectrum of a carbon fiber shifts with the applied stress on the fiber. In this paper, stresses of carbon fibers in short fiber reinforced composites were evaluated according to the shifts in Raman spectra. The stress levels of individual fibers in the composites could be evaluated by this spectroscopy. The change of stress distribution along the fibers by deformation could also be measured, connected with the microscopic failure in the composites. It has become clear that the shifts in Raman spectra are directly related to the deformation and fracture of the short fiber reinforced composites.