This study aims to use graphene oxide to improve the strength properties of oil well cement. The fluidity, setting time, strength properties, and hydration products of oil well cement paste with different GO dosages (0–0.05 wt%) were investigated. The fluidity of cement paste decreased linearly with increasing GO dosage was indicated. The addition of GO not only promoted cement hydration but also reduced the R-index of portlandite, which densified the microstructure of hardened paste and thus enhanced the strength properties. By using a 0.02% dosage of graphene oxide, the compressive strength of oil well cement pastes increased by 28.9% and 11.1% at 1 day and 28 days, respectively. Meanwhile, the flexural strength of cement paste increased by 72.5 and 34.1% compared to control. The enhancement of strength properties reduces the brittleness of oil well cement pastes, and improve wellbore integrity and cementing quality.