The invention relates to grease and a preparation method thereof, in particular to calcium sulfonate complex grease and a preparation method thereof, which belong to the field of chemical technology. A formula of the calcium sulfonate complex grease includes, in weight percentage, 23.5-35.5% of base oil, 32.0-45.4% of high alkalinity calcium sulfonate, 5-15% of calcium carbonate, 1.1-1.5% of alkyl benzene sulfonic acid, 2.5-3.5% of isopropanol, 3-6% of water, 1.9-2.7% of calcium hydroxide, 2-4% of 12-hydroxystearic acid, 1.75-2.25% of inorganic acid, 0.5-3.5% of thickening agent, and 0.1-5% of antioxidant. The calcium sulfonate complex grease has the advantages of high dropping point, fine rust and corrosion resistance, extreme pressure and wear resistance, fine mechanical stability, no hardening in long-term storage and long service life.