Abstract: A method for the XRF determination of carbon with OHM crystal as dispersion unit is described.Through adjusting circuit and crystal angle,the signal to noise ratio could reach 38.19 and 54.04 when the thickness of the FPC window film are 5μm and 0 6μm respectively.The results obtained show that the determination of carbon in white cast iron,graphite and SIC by XRF is fast,simple and accurate,and can meet the requirement of routine analysis.