In order to obtain the thickening agent used in fracturing fluid on the condition of ultra-high salinity and 210℃ high temperature，a terpolymer thickening agent APC-30 was prepared by acrylamide（AM），2-acrylamido-2-methylpropanesulfonic acid（AMPS）and acryloyl morpholine（ACMO）. The viscosifying performance，salt-tolerance and thermal stability of APC-30 were investigated. Furthermore，the temperature and shear resistance，viscoelasticity and breaking property of the gel fracturing fluid with the combination of APC-30 and organic zirconium crosslinking agent BPA were studied. The results showed that APC-30 which synthesized on the condition of 70∶24∶6 monomer mass ratio of AM/AMPS/ACMO，0.4% composite initiator K₂S₂O₇-NaHSO₃ and 1.2% chain transfer agent HCOONa presented a better viscosifying performance，thermal stability and salt resistance than binary polymer thickening agent AP-30. The viscosity retention of APC-30 was 35% under the condition of 450 g/L salinity，200℃ temperature and 170 s^-1 shear rate. The introduction of morpholine group with six-membered heterocyclic structure could obviously improve the temperature and shear resistance of fracturing fluid gel. The viscosity of APC-30 fracturing fluid gel was 175.8 mPa·s after shearing at 210℃ and 170 s^-1 for 2 hrs. The APC-30 fracturing fluid gel had the characteristics of high elasticity，low viscosity as well as excellent sand carrying capacity. The broken liquid of fracturing fluid had low residue content and easily backflow. The new type fracturing fluid could be used for fracturing operation on site.