This work proposed to use silica fume(SF)as a mineral admixture to study the effects of SF on the early mechanical properties and microstructure of magnesium phosphate cement-based grouting materials(MPCG).The results showed that the main hydration product of MPCG was struvite-K(KMgPO4·6H2O),and the addition of 6%SF could reduce the generation of microcracks in matrix.The compressive strength and water resistance of MPCG were improved by making the MPCG matrix more compact.At this time,the compressive strength at 7d reached 11.7 MPa after curing in air.