Magnesium phosphate cement (MPC) is a kind of rapid repairing cementitious materials, and it has many advantages, such as rapid setting, high early strength, high strength, and bonding strength and good durability. Firstly, we use the orthogonal test design method. By controlling the binder-sand ratio (B/S), molar ratio of magnesium and phosphate (M/P), and water-binder ratio, we find the MPC repair mortar benchmark optimal mixture. Afterwards, based on the optimal proportion of the MPC repair mortar, the influence of fly ash and slag on the compressive strength and flexural strength of MPC rapid repair mortar are studied. The results show that the optimum proportion of rapid repairing mortar is M/P=6∶1 and B/S=1∶1. Besides, the addition of fly ash can improve the strength of MPC mortar, especially the flexural strength. Thus, the MPC repair mortar blended with fly ash is suitable as a rapid repairing material. However, when the MPC mortar mixed with slag, the mechanical properties are not performing as well as the MPC mortar mixed with fly ash. In addition, the flexural strength of MPC mortar has close linearity correlation in the compressive strength. And there is no correlation between strength and factors including curing period, source of raw materials, sintering temperature, adding retarder or mineral admixtures, M/P ratio and water-binder ratio.