The purpose of this study was to investigate the effect of the content of hybrid nano-silica (NS) and nano-hexagonal boron nitride (h-BN) on the rheological properties and early mechanical strength of oil-well cement using response surface methodology (RSM). Based on the microstructures revealed by X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy, the modification mechanism of cement mixed with a hybrid of NS and h-BN in the early stage of hydration was studied. It was found that the rheological properties of fresh oil-well cement slurries with added NS and h-BN conformed to those of Bingham fluids. An increase in NS content worsened the fluidity of the cement, whereas the h-BN content did not affect its fluidity. The early compressive, flexural, and splitting tensile strengths at the end of the 3-day curing time increased by 12.33 MPa/47.24 %, 1.88 MPa/29.01 % and 1.24 MPa/53.22 %, respectively. The pozzolanic reaction of NS begins to occur in the early stages of cement hydration. The synergistic effect of the added NS and h-BN increased the density of the early hydration product of the cement. The h-BN mainly enabled the bridging, filling, and crack-resistant effects in the early oil-well cement.