The present article adopts wavelength-dispersive X-ray fluorescence spectrometry to measure elements of P, S and Cl in 98 engine oil samples from America, Germany and Japan and including SM, SN, CI and CH API grade. Proportional relationship of Zn/P, S/Mo and Ca/Mg illustrated the correlation between experimental data and additive contents. The experiment indicates that the concentration levels of Zn, P, Ca, S, Mg and Mo were 0.09%~0.17%, 0.07%~0.15%, 0.13%~0.43%, 0.20%~0.47%, 0.04%~0.15% and 0.01%~0.05% respectively, among which the Ca, S, P and Zn were the main elements of engine oil, Mg and Mo exist in high quality level engine oil, while Nb, W, Ti and Na were present in individual engine oil.