In most low-permeability reservoirs producing regions of the world currently, for pressure continuous increase in the water-injection process is becoming increasing important issues when water flooding is conducted. In this work, a novel hydrophobic silica nanofluid (SNF) through modified by triethoxy(vinyl)silane (TVS) is adopted to adsorb on the surface of core so as to acquire hydrophobicity and decrease the water-injection pressure. Fourier transform infrared (FTIR) spectroscopy shows that methyl headgroups are successfully grafted on the surface of silica nanoparticles (SNP). The decrease of SHN (SHN) certifies the success of modification. Dynamic light scattering (DLS) result reflects that the modified SNF has excellent hydrophobicity and superior dispersibility. The wettability transformation of core surface from hydrophilic to lyophobic is determined by the water contact angles. The results of laboratory displacement tests show that the SNF has the remarkable pressure-decreasing ability due to adsorption on the surface of core.