The invention provides a magnesium alloy jet printing sizing and a preparation method of the magnesium alloy jet printing sizing. The magnesium alloy jet printing sizing comprises, by weight, 5-50% wt% of magnesium alloy particles, modified polylactic acid particles accounting for 10-40% of the mass and the balance assistants. The assistants are composed of a solvent, a consistence modifier, an active agent and a thixotropic agent. The magnesium alloy particles are AZ31 magnesium alloy, and the particle size of the AZ31 magnesium alloy is 25-38 microns. The preparation method of the magnesiumalloy jet printing sizing comprises the steps that the solvent and the consistence modifier are weighed, fetched, mixed and stirred, the thixotropic agent and the active agent are added in the mannerof shearing through a three-roller machine, polylactic acid, nano-hydroxyapatite, the solvent and a dispersing agent are weighed, fetched and mixed, and then the magnesium alloy particles and the modified polylactic acid particles are weighed and fetched and mixed with the assistants. By the adoption of the technical scheme, the modified polylactic acid particles of the specific particle size areadded, in this way, when the sizing is stressed and slides, the small particles lubricate the large particles of the magnesium alloy, and therefore the jet printing performance of the sizing is improved.