Abstract: By combining the FactSage theoretical calculation and experiment,the change of carbon-thermal reduction reaction system of phosphate ore with different ratios of silicon to calcium was studied.The thermodynamic results show that under the vacuum condition of 1 Pa,the volatilization rate of phosphorus element in the gas phase reached its maximum at 1250℃.When the SiO₂/CaO ratio was 0.4 and 0.8,the volatilization rate of phosphorus in the gas phase increased compared with the addition of SiO₂.Continued addition of SiO₂ would inhibit the volatilization of phosphorus.The calculated results show that under the conditions of 1Pa and 14%carbon content,calcium fluorophosphate not only reacted with SiO₂,but also continuously defluorinated itself.The addition of SiO₂ could significantly increase the reduction rate of phosphate ore and the volatilization rate of phosphorus.When the SiO₂/CaO molar ratio was 0.8,the promotion effect of phosphorus reduction was most obvious.When SiO₂was excessive,it would indirectly reduce the grade of P₂O₅ in the ore.It resulted in a reduction in the driving force of the reduction process,which would make phosphorus the volatilization rate reduced.