Abstract: Research and development of the seawater-based fracturing fluid system is the key technology to reduce the cost of offshore fracturing construction， improve the construction efficiency and fracturing scale. A polymer instant seawater-based viscosifier was synthesized by the plate polymerization process，and the seawater-based fracturing fluid system with a temperature resistance of 140 ℃ was established. The viscosity of fracturing fluid was 78 mPa·s after shearing for 2 h at 140 ℃ and 170 s^-1. After breaking，the viscosity changed to 3. 5 mPa·s，the surface tension was 25. 38 mN/m，the interfacial tension between the breaker and kerosene was 1. 7 mN/m，and the average residue content was 70. 75 mg/L. All indexes of fracturing fluid meet the requirements of field application.

Key words: seawater-based fracturing fluid, instant fracturing fluid, salt-resisting viscosifier, offshore field