The interest in the application of nanofluid in reducing injection pressure has been increasing especially for tight reservoirs. In this work, a new type of hydrophobic carbon nanofluid was prepared and the pressure-reducing performance was investigated. The results of particle size distribution, zeta potential, and transmission electron microscopy image showed that the dispersion of nanofluid was uniform and stable. In addition, the hydrophobic carbon nanofluid showed excellent antitemperature and antisalinity property. The contact angle of oil-wet glass slide can range from 45 to 89° after it adsorbs hydrophobic carbon nanoparticles (HCNPs). The atomic force microscope tests showed that the core surface roughness was reduced about 16.67%. The core flooding tests showed that the pressure-reducing rate of 0.15 wt % HCNP nanofluid can reach 17.00%. HCNPs show good performance in reducing pressure and have a broad application prospect in oil field development.