Abstract: In this article the relative peak absorption technique for the determination of degree of atomization in air-acetylene flame was proposed and its theoretical basis was disccussed as well.The degree of atomization of Na, Mg,Cr and Mo in air-acetylene flame was measured with Cu as a reference element. The effect of the flame composition and height on absorbance for four elements and the degree of atomization of Na and Mg were investigated. It was shown that both of these two factors can influence the degree of atomization, but the influence of flame composition is larger than that of its height. Therefore, the degree of atomization is a relative value which varies with the condition of measurement.