Abstract: In response to the water quality characteristics of high salinity and high hardness oilfield, designs the “sodium silicate+dispersant” composite solution which can react with calcium and magnesium ions in oilfield injection water to quickly generate precipitated particles with a minimum particle size of less than 100 nanometersor. Adjusting the concentration ratio of sodium silicate to dispersant can change the agglomeration degree of nanoparticles, make the initial particle size controllable within 60.4 nm～3.85 μm, and make the dispersion time controllable within 2 h～6 d to accommodate reservoirs with different permeability. After aggregation of dispersed particles, the final size of aggregates exceeds 70 microns which can effectively block high permeability layer and realize deep fluid flow steering.Field tests of the technology have been carried out in the South China Sea oilfield. After 192 days of continuous operation, the average water injection pressure increased by 2.9 MPa, and the cumulative oil increase exceeded 6,200m³. The effective period was more than 4 months.