Abstract: A method for the determination of 21 major, minor and trace elements in coal and coal ash samples by inductively coupled plasmaoptical emission spectrometry (ICP-OES) was reported in this paper. The sample was digested with mixed acid of HCl-HNO3-HF-HClO4 and 21 elements in HCl medium were simultaneously determined by ICP-OES. The leaving peak background correction and interference coefficient methods were used for eliminating the interference. The detection limits for the elements were 0.03～5.6 μg/g. The method has been applied to the determination of 21 elements in National Standard Reference Materials and the results are in agreement with certified values with precision of 0.5%～3.6%RSD （n=11）.