A water-soluble polymer thickener BCG-1 was synthesized by using acrylic acid，acrylamide，cationic unsaturated monomer and anionic unsaturated monomer as mainly polymeric monomers，sodium dodecyl benzene sulfonate as emulsifier and ammonium persulfate-sodium bisulfite as initiator system. BCG-1 could be able to swell in seawater ，and the apparent viscosity of seawater solution with BCG-1 dosage of 0.6% was greater than80mPa·s. The seawater-based fracturing fluid was prepared by using the thickener and other related additives ，the formula was obtained as follows: 0.6% BCG-l+0.4% metal ions chelating agent BCG-5 + 0.3% viscosity synergist B-55+ 0.1% temperature stabilizer B-13+ 0.02%～0.05% capsule gel-breaker BCG-10. The fracturing fluid had no precipitation and the apparent viscosity changed little after being laid up for a week at 30℃，indicating a good stability at normal temperature. The viscosity of the fracturing fluid remained at 46.9 mPa·s after shearing at 170 s^-1and 140℃for 60minutes，showing good temperature and shearing tolerance. The falling ball viscosity was 4534.7 mPa·s，showing goodcarrying capacity. And it could be completely gelout，the content of residue was less than 5 mg/L. The surface tension of broken gel liquid was less than 26mN/m. The damage of broken gel liquid on flow conductivity of support crack diversion was below8% ，which completely possessed the performance characteristics of clean fracturing fluid.