The invention relates to a halogen-free scaling powder used for a lead-free solder paste and a preparation method thereof. The halogen-free scaling powder used for the lead-free solder paste is characterized by being composed of the following components by weight percent: 25-55% of modified rosin, 3-12% of active agent, 0.1-3% of surface active agent, 2-6% of thixotropic agent, 0.01-3% of antioxidant, 0.1-2% of release agent, 30-50% of solvent and 0.1-5% of oil wetting agent, wherein the scaling powder does not contain halogen; the activity of the scaling powder can be obviously improved through adding organic carboxylic acid and hydroxy carboxylic acid as the active agent, and combining the active agent with the surface active agent; and in addition, the oil wetting agent is used, so that a layer of thin continuous oil membrane is enabled to cover the surface of a welding spot in a whole reflow soldering technological process of the solder paste, thereby playing an oxygen insulating function, and greatly improving the expansibility and the wetting property. The solder paste prepared by the scaling powder provided by the invention and a tin-silver-copper lead-free solder has the advantages of being good in printing performance, clean in demoulding, good in solderability and strong in wettability, having no penetrability corrosion in a bronze mirror after soldering, being high in soldering spot reliability and excellent in mechanical property, and capability of satisfying the high reliability requirements of high-end electronic products.