In order to meet the demands for seawater-based fracturing fluid under the temperature of 180℃，a thickener SWF-T180 of associated polymer was synthesized with acrylamide， acrylic acid， 2-acrylamido-2-methyl-propanesulfon-icacid， N-vinylpyrrolidone， dodecanol maleic anhydride sodium and N-hexadecylacrylamide as raw material， and ammonium persulfate-sodium sulfite as initiator. The increasing viscosity，salt-tolerance，swelling，temperature-resistance of SWF-T180 and the performance of seawater-based fracturing fluid prepared by SWF-T180 were evaluated. The results showed that SWF-T180 had an obvious viscosity enhancement effect. When the dosage of SWF-T180 was greater than 0.6%，the viscosity of the fluid increased rapidly. SWF-T180 had good resistance to salt，calcium and magnesium with large dissolving capacity. The viscosity of SWF-T180 after dissolving in seawater for 8 minutes reached 84.3% of its ultimate viscosity. The temperature resistance of SWF-T180 was up to 180℃. The viscosity of seawater-based fracturing fluid composed of 1% SWF-T180 and 0.6% crosslinking agent was 60—70 mPa·s under the condition of 180℃ and 90 minutes shearing time. SWF-T180 had a good shear recovery feature，which met the requirement of offshore reservoir fracturing operation at 180℃.