In order to improve the thermal endurance and shearing resistance of conventional thickener，a hydrophobic associating crosslinking acid thickener AAG4 was synthesized by using acrylamide（AM），dimethyldiallyl ammonium chloride（DMDAAC）， acrylic acid（AA），2-acrylamido-2-methylpropanesulfonic acid（AMPS）and hydrophobic monomer YD-D10 as raw materials through radical aqueous solution polymerization process. The synthesis process of AAG4 was optimized，the structure was characterized，and the properties of crosslinked acid prepared with AAG4 was investigated. The results showed that the optimum preparation condition of AAG4 was obtained as follows：0.01% initiator azodiisobutyl hydrochloride（V040），0.04% ammonium sulfate and sodium bisulfite in mass ratio 1∶1，0.42% YD-D10，35℃ reaction temperature，6 hours reaction time. AAG4 had good thermal stability. When the dosage of hydrochloric acid was 20%，AAG4 had good crosslinked property with organic zirconium cross-linking agent and the crosslinked solution possessed excellent temperature and shearing resistance. The viscosity of acid was 82 mPa·s after shearing for 1 h at 120℃ and 170 s-1 . The reaction rate of crosslinked acid with natural core was much lower than that of hydrochloric acid at 90℃，and the retarding rate of crosslinked acid was 97.3%，indicating good retardative property. The final dissolution rate of natural core by crosslinked acid was equivalent to that by 20% hydrochloric acid at 30℃. The acid pressure construction effect on site was good，which could realize the depth transformation of carbonate reservoir at high temperature.