Abstract: In order to reveal the influence mechanism of lignite dosage and roasting temperature on the effect of CaCO3, the direct reduction-magnetic separation tests were carried out for a foreign high-phosphorus oolitic hematite with lignite and CaCO 3 as reductant and dephosphorization agents, respectively. Thermodynamic calculations, XRD and SEM-EDS analysis showed that the effect of CaCO 3 was the synergism of CO2 and CaO generated by the decomposition of CaCO3. The main role of CaO is to promote the formation of apatite from the part of the phosphorus in the iron mineral,which is in the form of Fe3PO7, and inhibit the reduction of apatite and the formation of iron olivine and iron spinel. CO2 can promote the gasification of coal and accelerate the reduction of iron oxides. The lignite dosage and the roasting temperature affect the degree of response of CaO,which in turn will affect the effect of CaCO3. Due to the high degree of melting in the roasting process at low lignite calculations or high roasting temperature,the solid phase reaction of CaO can be promoted,so the effect of CaCO3 is good. Experimental studies have found that the direct reduction roasting effect was good at roasting temperature of 1 200 °C,the lignite dosage of 20% and CaCO3 dosage of 28%,in which the dephosphorization rate was as high as 92%.