Different doses of electron beam was imposed on polyacrylonitrile(PAN) precursor fibers before the fibers were stabilized. The effect of electron beam irradiation on the chemical structure, orientation degree, surface morphology and tensile properties of PAN precursor fibers were characterized by use of fourier transform infrared spectroscopy (FTIR), tensile test and scanning electron microscope (SEM), respectively. The results showed that the extent of cyclization and orientation degree was increased firstly and decreased later. The surface morphology of PAN precursor fibers was smoother when the irradiation doses 150kGy and 200kGy. Tensile strength of the fibers was increased first and decreased later. The change of tensile strength might be in correlation with the changes of extent of cylization, orientation factor and surface morphology.