Abstract: Aiming at the characteristics of high porosity, high permeability and loose sandstone reservoirs in L Oilfield of Bohai, a set of instant dissolved seawater based fracturing fluids have been developed, and the properties of quick solubility, temperature resistance, shear resistance, leak off, gel breaking and core damage were evaluated. The experiment result shows that the percentage of dissolution reached 92.3% when SWF-SRG dissolved and swelled in seawater for 5 minutes, which meets the requirements of continuous mixing in fluid preparation; after shearing for 120 minutes at the reservoir temperature, the viscosity of the instant dissolved seawater based fracturing fluid is greater than 50 mPa·s, which meets the requirements of carrying sand in site fracturing operation; the fracturing fluid has the advantages of high wall filtration coefficient, easy gel breaking and low reservoir damage, which is suitable for offshore loose sandstone fracturing. The continuous mixed fracturing of the dissolved seawater based fracturing fluid has been successfully applied in L Oilfield, the maximum mixing speed of 4.3 m³/min, the maximum sand ratio of 60%, the maximum sand addition of 51.1 m³, achieved the construction success rate of 100%, which greatly improves the efficiency of offshore fracturing operation, and provides technical support for large-scale offshore fracturing.