The Mosbauer spectra of oxide scale of steel formed during heating have been studied. The results showed that （a） the dominating composition in the scale is FeO （ >70%）

Fe3O4 （-15% ） and some α-Fe2O3 （< 10% ）; （b） burning emulsified fuel oil would increase the ratio of Fe3O4 to FeO and toα-Fe2O3 in the oxide scale

especially in its inside layer.The calculation of equilibrium constants indicated that composition of the scale can vary with the change of PH2O/PH2 in the gaseous phase

which corresponded with the results of the Mossbauer measurement

thus satisfactorily explaining why the scale composition varied and the scale formation was decelerated when adopting emulsified fuel oil.