The invention relates to a silicon boride enhanced FeMnSi micro-nano powder core wire for laser additive manufacturing and a preparation method thereof. The powder core wire is characterized by beingprepared from a rare earth enhanced micro-nano powder core wire composed of micro powder which accounts for 28-36% by mass of the whole powder core wire and consists of manganese and silicon and silicon boride nano powder which accounts for 2-4% by mass of the whole powder core wire, and an iron sheet which accounts for 60-70% by mass of the whole powder core wire, totaling 100%. The preparation method primarily comprises the following steps of micro-nano powder preparation, skin formation and powder filling, and closing and drawing to form the thread. The FeMnSi micro-nano powder core wire prepared by the preparation method provided by the invention as a material for laser additive manufacturing has the characteristics of being small in shape memory function loss, high in forming precision and the like, solves the problems that the utilization ratio of powder as the additive manufacturing material is low at present and the like, and also solves the problems that function loss is moreeasily caused as laser energy needed by taking a solid wire as the material for laser additive manufacturing is relatively high and the like.