<p>The rheological behavior of cement grouts often deteriorates significantly with increasing temperature, particularly during grouting in deep formations. Although traditional superplasticizers are effective in improving the flowability of cement grouts, they can also negatively affect its setting. Modified nanomaterials, designed to address the challenge of excessive specific surface area, present a promising alternative. In this study, modified graphene oxide (MGO) is synthesized via free radical polymerization to enhance both the fresh properties and strength performance of cement grouts at elevated temperatures. Polymer chains from Methylallyl Alcohol Polyoxyethylene Ether (MAPE) are copolymerized and covalently grafted onto the hydrophilic hydroxyl and carboxyl groups, to form the MGO. The grafting rate of MGO can be considered around 29% estimated by analyzing the mass loss. Incorporating 0.05 wt% MGO significantly improves the initial rheology of cement grout at elevated temperatures, reduces its time-dependent behavior, and effectively delays the setting, due to the steric hindrance and electrostatic repulsion provided by the polymer chains grafted onto the MGO. Furthermore, MGO can also effectively enhance the strength performance and density of hardened cement grouts under high temperatures. The findings suggest that the MGO can improve the injectability of cement grout under high ground temperatures, thereby enhancing grouting quality in deep underground applications.</p>