This study investigated the mechanical properties of cement mortar with highly dispersed graphene oxide after exposure to 105, 200, 300, and 450℃. First, GO was uniformly dispersed in the cement matrix with the aid of polycarboxylate-based superplasticizers. The results showed that the incorporation of 0.04wt% dispersed GO can improve the flexural strengths and compressive strengths of cement mortar. For cement mortar with 0.04% GO (by weight) (MPG) exposed to temperatures of 105, 200, 300, and 450℃, the flexural strengths were 10%，7.6%，11.43%，16.64%, and 11.67% higher than that of cement mortar without GO (MP), respectively. And the compressive strengths of MPG were 13.95%，3.89%，6.38%，11.14%, and 4.15% higher than that of MP. According to the composition and structure analysis of hydration products, the incorporation of dispersed GO improved the hydration degree. The MIP results showed that the addition of dispersed GO suppressed the coarsening of the pore structure, improved the pore structure and reduced the porosity after exposure to high temperatures. SEM results revealed the significant improvement in the interfacial transition zone in cement mortar.