The lowest assimilation temperature is usually used as a terminal system index to characterize assimilation reactions between iron ores and CaO. However, this characterization does not take into account assimilation speed and heating rate. In order to adopt several indexes to evaluate the characteristics of the assimilation reactions, this article introduces an assimilation characteristic parameter by adopting the Van't Hoff's law and making full use of data obtained in the high temperature assimilation process of iron ores. The characteristic parameter, which considers assimilation speed, heating rate, assimilation temperature and the effect of temper-ature on assimilation speed, can characterize assimilation reactions between iron ores and CaO, including assimilation starting tempera-ture, assimilation time, assimilation finishing temperature, etc. Moreover, it is based on the practical production temperature of sinte-ring ores. Because of integrating much more important information in the assimilation process of iron ores, this parameter can compre-hensively reflect the assimilation properties of iron ores. Although the same or similar results are obtained by the two methods, com-pared with the conventional method by only considering the lowest assimilation temperature, the new method can find out assimilability differences of different iron ores in further analysis.