The invention discloses a high temperature resistant cross-linked acid thickening agent and a preparation method thereof. The high temperature resistant cross-linked acid thickening agent is prepared by polymerizing three monomers, namely, 2-acrylamide-methylpropanesulfonic acid monomers, acrylamide monomers and N,N-dimethyl acrylamide monomers; a co-solvent, a chain transfer agent, a complexing agent, an oxidation and reduction initiating agent and an azo initiator are added in the polymerization reaction; then, the thickening agent is obtained by granulating and drying. The high temperature resistant cross-linked acid thickening agent disclosed by the invention is simple in preparation process, can be synthesized at a relatively low temperature easily and effectively, and has the characteristics of high temperature resistance, shear resistance, good retardance, and soluble performance in acid; a cross-linked acid-liquid system is prepared by the high temperature resistant cross-linked acid thickening agent and auxiliaries, such as a cross-linking agent, and can be applied to acidizing construction at 180 DEG C; secondary damage can be lightened effectively; the flow conductivity of an acid corrosion fracture and the penetration distance of an acid are improved effectively; the purpose of deeply acidizing is achieved.