Abstract: Samples were excited by pulse laser and plasma was formed at atmospheric pressure. The technique of laser induced breakdown spectroscopy(LIBS) was applied to analyzing the carbon content in the samples. The matrix element Si was selected as internal standard, calibration curves were drawn respectively using the peak intensity of carbon line and the intensity ratio of carbon line and silica line. The fitting degree of two different calibration curves, signal reproducibility and the accuracy of calibrated values were analyzed. The results of the analysis show that the intensity ratio method seems more adequate than the peak intensity method for establishing the calibration cures.