Modified magnesium phosphate cement mortar and preparation method thereof

The invention discloses a modified magnesium phosphate cement mortar, which is composed of the following components: magnesium oxide, potassium dihydrogen phosphate, a composite retarder, sand, silica fume and water, wherein the molar ratio of magnesium oxide to potassium dihydrogen phosphate in the modified magnesium phosphate cement mortar is 4: 1-6: 1, and the addition amount of the composite retarder is 3-10% of the total mass of magnesium oxide and potassium dihydrogen phosphate; the mass ratio of the silica fume to the total mass of the magnesium oxide, the potassium dihydrogen phosphate and the silica fume is 5%-20%, the mass ratio of the sand to the total mass of the magnesium oxide, the phosphate and the silica fume is 1: 1, the magnesium oxide, the potassium dihydrogen phosphate, the composite retarder and the silica fume jointly form a gelling component, and the mass ratio of the water to the gelling component is 0.2-0.25. The modified magnesium phosphate cement mortar disclosed by the invention is