The invention relates to a magnesium phosphate cement base fiber composite material and a preparation method thereof. The magnesium phosphate cement base fiber composite material is composed of following components in parts by weight: 516.2 to 823.4 parts of heavily burnt magnesia, 438.7 to 699.8 parts of potassium dihydrogen phosphate, 31.0 to 49.4 parts of borax, 159.2 to 636.6 parts of fly ash,15.6 to 26.0 parts of polyethylene alcohol fiber, 248.3 to 325.0 parts of water, and 0 to 546.9 parts of quartz sand. The magnesium phosphate cement base fiber composite material has the characteristics of high ductility, strain-hardening, and multi-crack stable cracking damage, moreover, the work performance is good, the early strength is high, and the volume stability is excellent. In the priorart, a conventional cement base engineering material has the shortages of large shrinkage, long maintenance period, and low early strength, at a low temperature, the engineering material cannot be cured or hardened, and the binding force between the engineering material and a structure is weak, and the provided composite material solves the problems mentioned above, and has an important application value.