As the proportion of natural lump ore used in blast furnace is gradually increasing, the evaluation on its decrepitation index (DI) becomes more and more important. In this paper, a new method for evaluating the heat cracking index of lump ore under BF ironmaking through a series of experiments is proposed, and the influence mechanism of such 4 factors including sample particle size, reaction atmosphere, reaction temperature and time on the decrepitation behavior of lump ore is explored. The results show that: 1) after the standard decrepitation of lump ore, there is a large number of cracks inside with local aggregation, this part is very easy to form powder by extrusion and friction in the blast furnace, and the ability of this process to form powder is the dynamic DI of lump ore; 2) the best parameters for the test of dynamic DI of lump ore: sample particle size is 20~25 mm, reaction temperature is 900 °C, reducing atmosphere, and reaction time is 60 min; 3) the standard heat cracking indices(DI_-6.3mm) of lump ore A and B are 11.27% and 6.10%, respectively, while the dynamic heat cracking indices(DI_-6.3mm) of lump ore A and B are 18.31% and 15.35%, respectively, based on the above test conditions, which are not significantly different from each other.