Zwitterion guar 2-hydroxyl-3-（N，N-dimethylglycine）propyl guar gum（HDPG）as high temperature thickener，used for seawater based fracturing fluid，was synthesized from guar and（2-hydroxy-3-chloride）-propyl dimethylamino acetic acid. The effect of dosage of etherifying agent，sodium hydroxide and etherification temperature，etherification time on the substitution degree was studied，and the swelling property，shear resistance property，and break character of HDPG were researched. The optimum reaction condition of thickener was obtained as follows，molar ratio of etherifying agent to guar was 0.18∶1，molar ratio NaOH to guar was 0.125∶1，the etherification temperature was 70℃，the etherification time was 6 hours，the substitution degree of HDPG was 0.43. On the condition of stirring rate of 500 r/min and the swelling time of 10 min，the viscosity of 0.5% HDPG solution reached 85% of final viscosity，which met the requirement of continuous mixing. The viscosity of seawater base fracturing fluid prepared by synthesized thickener and self-made crosslinking agent was above 50 mPa·s at the temperate of 170℃ after sheared for 120 min at the shearing rate of 170 s^-1，which indicated that the seawater based fracturing fluid had good shear resistance. In addition，HDPG seawater base fracturing fluid had good gel-breaking performance，the viscosity of gel breaking liquid being of 1.36 mPa·s，and the residue content being of 326 mg/L.