Abstract: The variation of element analysis results related to the diameter of round-bar specimens by Electric Spark-Direct Reading Spectrometry was uncovered during experimental work. A series of specimens, with diameters of Φ25 mm, Φ12 mm, Φ8 mm, Φ6 mm, Φ4 mm and Φ3 mm, were prepared from a 40 mm thick alloy steel plate. All the round-bar specimens were analyzed by using direct-reading spark spectrometry. The results indicate that the specimen with the smallest diameter has the highest content reading of C, S, Mn, P, Cr, Ni, Cu and Sn, slightly lower content reading of Si and low content reading of Mo and V. The variation of content readings is related to the volatility and occurrence form of the target element. In order to correct the results, a curve interpolation method was applied. A CRM was analyzed and corrected, the element deviation between the content result and certified value was less than the tolerance between laboratories (R), and the feasibility of the method was confirmed. This method is suitable for round-bar specimens with more than Φ3 mm in diameter.