The invention relates to an inverse emulsion polymer thickener for a fracturing fluid and a preparation method thereof. The thickener is polymerized by water, 2-acrylamidyl-2-methyl sodium proparesulfonic acid liquid with mass fraction of 50%, alkyl acrylamide, acrylamide, a cationic monomer, N, N-methylene bisacrylamide, a tween-80 emulsifier, ethylene diamine tetraacetic acid disodium salt, 30% sodium hydroxide, white oil, acrylic ester, a span-80 emulsifier, sulfite, a peroxysulphate initiator, a water-soluble azo initiator and OP-15. According to the invention, raw materials are industrial products, and purification is not needed before reaction; polymerization is initiated by initiators by adding a complexing agent, and the preparation process is simple; the thickener provided by the invention is fast in dispersing, easy to prepare, free from pollution and harm, small in use level and good in stability, in particular resists high temperature of 220 DEG C, and is suitable for fracturing a high-temperature stratum; and the thickener is higher in shear resistance, can meet the fracturing construction of high flow, has high sand carrying performance, and is free from residue and is not harmful to the reservoir.