The present invention discloses a fracturing magnesium alloy pressure holding ball and a preparation method thereof. The fracturing magnesium alloy pressure holding ball comprises an alloy ball body and a coating covered on the alloy ball body, wherein the alloy ball body comprises 15-20 wt% of Al, 5.5-15 wt% of Cu, 0.1-1.9 wt% of Zn, 0.6-1.4 wt% of Zr, and the balance of being Mg, the costing has two layers, one of the two layers is an organic coating being subjected to chemical conversion film treatment and has a thickness of 1-3 [mu]m, and the outer layer is a heat-resistant organic coating and has a thickness of 5-10 [mu]m. According to the present invention, the protection film having a certain thickness is formed on the pressure holding ball surface through the chemical conversion film treatment and the heat-resistant organic coating spraying so as to control the initial decomposition rate of the pressure holding ball; and the prepared pressure holding ball has a certain pressure holding strength and controllable fast-corrosion-decomposition capacity, and can meet the pressure holding strength and the fast corrosion decomposition performance on the pressure holding ball during the multi-stage sliding sleeve staged fracturing technology.