Abstract: Magnesium phosphate cement (MPC) is a new type of cementitious material that has the advantages of fast hardening, early strengthening, and stable volume, and is used in the field of structural repair and reinforcement. In this paper, Magnesium phosphate cement mortar (MPCM) was produced and steel fiber reinforced magnesium phosphate cement composite (SFRMPCC) was made by fiber toughening, and the curing temperature (20°C, −15°C and −30°C) and curing age (6h, 1d, 3d, 7d, 14d and 28d) were taken as variables. The strength development of MPCM and SFRMPCC under negative temperature curing was analyzed by cubic compressive and splitting tensile strength. The results show that MPCM and SFRMPCC could still harden and obtain high strength at the early age even under the condition of negative temperature curing at −30°C. In order to further clarify the strengthening mechanism of SFRMPCC in negative temperature environment, the effects of different curing conditions and loading conditions on the compressive strength of SFRMPCC were studied by changing the curing temperature and test temperature of the specimens, and the influence mechanism of negative temperature environment on the compressive strength of SFRMPCC was analyzed from the microscopic level.