Abstract: A set of CRM′s with values of wC% ranged from 0.002% to 0.03% was analyzed for their carbon contents with a direct reading AES under the specified working conditions. A statistical study was made based on data obtained, i.e., the values of wC% of each of the CRM′s and their statistics and levels of accuracy and precision of the method for determination of ultra-low carbon in steel sheets were assessed. It was shown that: ① accuracy of the analytical results was affected by the matrix background of individual sample and standardization condition of the instrument, it is advised to choose CRM′s having similar composition with the sample for calibration of instrument and rational condition of standardization;② in the range of carbon content concerned, only small differences among values of S% (either for n=5 or 10) were obtained with difference of extreme values of 3×10-4%, but significant differences of values of RSD% were observed with min. and max. values of 2% and 21% respectively;and ③ range of fluctuation of systematic error (or of accuracy) for determination of carbon content at the magnitude of 10-5 attained to values ranged in ±1×10-4%.