The invention relates to the field of magnesium matrix composites, in particular to a high performance magnesium matrix composite based on laser 3D printing forming and a preparation method thereof. The high performance magnesium matrix composite comprises, by weight, 2-5% of monatomic silicon particles, 6-8% of LiH, 1-2% of CaH, and the balance high-purity magnesium powder. The problem of the evaporation and oxidation of magnesium alloy powder in the forming process can be effectively reduced, so as to ensure a precision forming manufacture of high performance magnesium alloy, and also a method for the preparation of magnesium alloy powder specially for laser additive manufacturing is provided.